Page 1

Conserving Bogs

Introduction

1


Conserving Bogs

Introduction

INTRODUCING THE BOG MANAGEMENT HANDBOOK HANDBOOK FORMAT This Handbook is, above all, a practical manual: a cookbook of methods and techniques to help people effectively manage and conserve bogs. The handbook has been written with peatland conservationists in mind although it is as useful to any land manager who has control of bogland. Above all, it is hoped that this Handbook can inspire and guide people towards bog conservation. The Handbook has been laid out in 6 parts (see Figure 1.1). The first part concerns the values and uses of bogs. The positive values considered here include: biodiversity and landscape, a carbon store, nature reserves, their peat archive and catchment hydrology. Alternatively, bogs are viewed as an economic resource or as wasteland to be ‘improved’. Only recently, has the former attitude become more prevalent; many bogs have suffered considerable damage. These uses are also outlined in Part 1. By looking at the damaging uses bogs have been put to, a damage assessment can be made. A detailed description of various damaging activities is, therefore, included in Appendix 1. This allows a detailed site assessment to be made as a tool for management planning (see Part 3). Figure 1.1 The Handbook Structure. Appendix 1: Site Assessment of Bogs from the Damaged Sustained

Part 1: The Values and Uses of Bogs

Part 2: Distribution and Ecology

Part 3: Planning Conservation Management

Part 4: Monitoring and Site Assessment

Part 5: Methods and Techniques for Management

Part 6: Links to bog conservation projects

2


Conserving Bogs

Introduction

In Part 2, Distribution and Ecology, an introduction to bog ecosystems is given. Sections on classification, distribution, raised and blanket bog and their formation, bog vegetation, bog hydrology and bog chemistry are laid out. These are all summaries and, if detail is required, specialist texts should be sought. Part 3 of the Handbook details the ways in which management plans should be prepared for bogs. The management plan format adopted is that developed by the Nature Conservancy Council and its successor bodies which is succinctly summarised in "Site Management Plans for Nature Conservation - A Working Guide" (NCC, 1988). The basic structure is re-stated before going on to show how this structure can be used for bog management. Given that each site has its own unique set of characteristics, guiding bog managers to effective management strategies is difficult. However, the types of damage bogs may have sustained are common across many sites and often require common solutions. Thus Section 3.3 describes the varying types of damage, ecohydrological effects that ensue and how the effects of such damage can be recognised. This section - Action Plan: Damaging Impacts and Solutions - forms the lynch-pin of the Handbook as it links damage (Part 1, Appendix 1) to the actual methods and techniques (Parts 4 and 5) which could be used for conservation management. Thus Section 3.3 gives a variety of options available to ameliorate the effects of damaging activities. Cross-linking of different sections in the Handbook is a common feature throughout. This allows managers, who come at the subject with differing levels of experience, to navigate through the volume at different speeds according to their knowledge. A manager with many years of experience could thus skip from a description of a particular type of damage straight through to necessary techniques extremely quickly. If one's experience is less, then it would be worth going through each section rather more slowly. It is important to remember, that the Handbook structure is defined by such cross-linking of sections (although contents and index lists are provided also). Each technique for monitoring and management is laid out in Sections 4 and 5 respectively; they effectively form the main parts of the Handbook. Techniques can be considered on their own and pages should be easily printable to be used in the field. Again, though, the reader should be aware of extensive cross-referencing to other parts of the Handbook. Management techniques may, for example, be cross-linked to a monitoring method designed to test the effectiveness of such management. Particularly useful cross-references take the reader to the final part of the Handbook.

MANAGING BOGS The ecologist looks at bogs as one of the most limiting of ecosystems - highly acidic, nutrient poor and, of course, waterlogged - and delights in their biodiversity and landscape. The climatologists consider the vast store of carbon that peat bogs contain and the effects that this must have on global carbon cycling. Archaeologists gain insights from the beautifully preserved organic remains. Environmental historians extract detailed records of human culture and environmental change. For many, bogs are a source of fuel, whilst for others bogs represent a profitable industry. Yet, all across the globe, bogs have been damaged and modified. In some countries such as the Netherlands and Germany, bogs have been destroyed leaving only fragmentary remains which give only a partial clue to the past watery richness of this once common landscape. In Britain and Ireland, the blanket bogs which envelop the north and west still remain although they are now much modified. In the lowlands, the raised bogs have become one of Britain’s rarest habitats - having been afforested, ‘reclaimed’ for agriculture and cutaway for gro-bags and the horticultural industry. 3


Conserving Bogs

Introduction

Only recently has society begun to recognise the true significance of Europe’s peat bogs. Gradually, nature protection has checked the progressive destruction of this natural asset. For many bogs, however, legislative protection is not enough. To conserve a site, management is needed. In Europe, conservation management of bogs was first practised in Holland and Germany. In the Netherlands, initial management works concentrated on preserving two semi-intact blocks, Engbertsdyksvenen and Bargerveen, in the 1960s. In Germany, management concentrated on rehabilitating industrially worked bogs. One of the first bog management works in Britain was carried out at Danes Moss (Mead, 1992) although fen management for conservation purposes has long been practised (e.g. at Wicken Fen since the 1890s). A devastating fire at Glasson Moss, a Nature Conservation Review site (Ratcliffe, 1977), spurred the Nature Conservancy Council to switch from protection to active management of the site. The success of the works at Glasson - the site now has some of the finest raised bog vegetation in Britain - demonstrates the potential of such management. An important impetus to peatland management came as a result of The Peatland Management Handbook (Rowell, 1988). As published material relating to peatland management was so scarce, Rowell culled much of the information for the Handbook directly from people interested in, or practising, peatland conservation management. Rowell's aims were to: review present knowledge, stimulate improved management and encourage an interchange of ideas and experience between conservation managers of peatlands. The Peatland Management Handbook proved to be extremely successful in achieving its aims and led to a flurry of bog management initiatives throughout the country. As Rowell realised, some of the techniques and methods presented were new and relatively untested. It was specifically noted that … some sections of the Handbook will become out of date quite rapidly … (p.2). To counteract this, the Handbook was designed to be easily updated. Today though, peatland management has moved on dramatically and a new Handbook is now required especially in the light of the Habitats Directive and the Biodiversity Convention which commit the British Government to conserving Britain’s biodiversity (see, for example, Juniper, 1994). In this volume, the focus lies on the management of ombrotrophic (literally: rain-fed) peatland systems only, i.e. bogs. In addition, there is an undisguised emphasis on conservation management of north-west European bogs, and in particular, British bogs. This is the result of the experience of the authors and of the data available.

A PLEA FOR GOOD REPORTING This Handbook is part of a process towards pushing forward the effectiveness of peatland conservation management. In Britain, Rowell's (1988) extremely useful Peatland Management Handbook laid the framework for a more professional approach to the subject. Projects such as EN's Lowland Peatland Project (1992-1996) and SWT's Raised Bog Conservation Project (1993-1995) have been networking information around the bog management community via workshops, reports, site visits, newsletters and, of course, long telephone conversations. The alliance of practical experience with academic research has brought bog conservation to a threshold. We are now in a position to move from crisis management - conserving our best sites - to reversing the progressive degradation of our peatland resource. If we are to achieve this, management will need further refining. Many techniques are still experimental and need evaluating. Evaluation can only be achieved if good records are kept and management is monitored to test its effectiveness.

4


Conserving Bogs

Values and Uses of Bogs

PART 1 THE VALUES AND USES OF BOGS This section looks at the ways bogs are valued and used. The section is split into the following sections: 1.1 INTRODUCTION 1.2 BIODIVERSITY AND LANDSCAPE 1.3 A CARBON STORE 1.4 BOGS AS AN EDUCATIONAL RESOURCE 1.5 NATURE RESERVES AND WILDERNESS AREAS 1.6 THE PEAT ARCHIVE 1.6.1 Introduction 1.6.2 The Nature of the Resource 1.7 CATCHMENT HYDROLOGY 1.8 PEAT EXTRACTION 1.8.1 Introduction 1.8.2 Domestic Cutting 1.8.3 Sausage Cutting 1.8.4 Baulk and Hollow (Sod) Cutting 1.8.5 Peat Milling 1.9 AGRICULTURE 1.10 FORESTRY 1.11 DEVELOPMENT 1.12 RECREATION 1.13 INDIRECT DAMAGE 1.14 DEGRADATION

5


Conserving Bogs

1.1

Values and Uses of Bogs

THE VALUES AND USES OF BOGS 1.1 INTRODUCTION A walk across the high ground of Britain nearly always involves a walk on water since the black 'soil' beneath, topped with a mat of cotton grasses and bog mosses, is peat. Given that wet peat is mostly water (90%), this is 'land' stretched to the edge of its definition; this is bogland. The bogs of the world span the high latitudes and parts of the tropics to cover 3% of the world's land area (Figure 1.1) - an area roughly equal to the size of India and Pakistan combined. Billions of tonnes of carbon are locked away in peatlands, a store that is twice that all the soil carbon of the world’s forests that cover 20% of the land surface. In some areas, peatlands dominate the landscape (Figure 1.2). In the north-west of Scotland blanket bog (see Section 2.3) covers the land, intertwining with the countries’ culture and economy. The rolling moorlands, the flavour of whisky, the dyes for tartan, and peat fuelled fires all relate to boglands (SNH, 1995). Bogs are variously viewed as a natural wonder or as an economic asset. The ways bogs are viewed is changing. At one time, bogs were highly regarded as a source of fuel and early spring 'bite' for cattle and sheep.

Figure 1.1 Mires around the world.

Fig 1.1. Distribution of mires around the world.

6


Conserving Bogs

Values and Uses of Bogs

1.2

Fig 1.2. An aerial view of the Flow Country, Scotland (Norman Russell). As the Agricultural and the Industrial Revolutions changed land practices, bogs came to be viewed as wasteland (Smout, 1996) or, in the uplands, as grouse moor. Gradually this view is giving way as people begin to appreciate the natural and cultural heritage of bogland. In this Part, the values of bogs, and the uses to which they have been put, are considered. This helps countryside managers both to assess the state of the bog in terms of the damage it has sustained and to consider what use the site should be put to. In effect, a site assessment can be undertaken to form the site description of a conservation management plan enabling land managers to understand the critical conservation features and how they need to be managed (see Part 3). Conservation management of bogs most often relates to ameliorating the effects of past damage. The types of damage sustained by sites are often widespread. By considering the ways in which the bog has been used and the damage ensuing from that use, solutions to countering the effects of damage can be formulated. The potentially damaging uses outlined below are considered in much more detail in Appendix 1. This Part is split into positive values (or ecosystem services): biodiversity, carbon-store, education, nature reserves, catchment hydrology and archive; alongside potentially damaging uses: peat extraction, agriculture, forestry, development, recreation. The effects of pollution and the cumulative effects of many small scale damaging activities are also discussed.

1.2 BIODIVERSITY & LANDSCAPE All across the northern altitudes, especially in Canada, Scandinavia and Russia, peatlands dominate the scene from the treeless blanket bogs of Scotland to the perma-frosted bogs of the North to the great forested bogs of the Siberian Taiga. In SE Asia, much of the remaining pristine rainforest grows on a blanket of tropical wood peat (Figure 1.3). Figure 1.3 Bogs throughout the world act as a significant part of global biodiversity. The remarkably specialised conditions of waterlogging, low nutrient status and high acidity combine to create a specialised flora and associated fauna. The carnivorous plants serve as an example (Figures 1.4 and 1.5). 7


Conserving Bogs

1.3

Values and Uses of Bogs

In European countries sundews (Drosera spp.) and butterworts (Pinguicula spp.) are found exclusively on mires. In North America, Fig 1.3. From an isolated granite extrusion, tropical peat swamp forest can be seen to stretch out to the horizon in every direction. However, this forest in Indonesia is threatened by huge logging and agricultural schemes (U.S. Dept of Agriculture). bogs nurture Sarracennia spp. whose leaves form funnels of enzyme-rich water to trap and digest insects. Most beautiful are the pitcher plants (Nepenthes spp.) of SE Asian peatlands. Alongside such specialised biodiversity, bogs are host to a large array of species which are found on other habitats. Dunlin and golden plover feeding on the mud-flats of eastern England, for example, may have spent their summer breeding on the peatlands of northern Scotland or the far northern tundra. Even the damaged raised bogs of the British lowlands, have a significant part to play in conserving regional biodiversity. By way of an example, a survey (Trabridge, 1994) of lowland raised mires in central Scotland revealed high numbers of skylark. This Fig 1.4. The carnivorous sundew, Drosera rotundifolia supplements its diet by catching insects on the sticky hairs of its leaves (YPP). species experienced a dramatic decline possibly because of intensive pesticide and fertiliser use. Raised bogs, despite damage, now host significant populations. Indeed, lowland bogs can form a wildlife oasis in an increasingly sterile (for wildlife) agricultural landscape.

Fig 1.5. Carnivorous pitcher plants, Nepenthes ampullaria, digest insects that fall into the watery enzyme-rich soup that collects in the base of the pitcher (Sandy Richard).

1.3. A CARBON STORE Peatlands are unbalanced ecosystems. The rate of addition of dead organic matter exceeds that lost by decay. As a consequence, layers of organic matter and water (forming peat) develop to form mires. Effectively, mires sequester carbon dioxide from the atmosphere and preserve the carbon as peat in the developing mire. Although peatlands are highly threatened in some parts of the world (England for example), they still cover a vast area globally (Joosten et al., 2009). This huge area of peatland thus represents a gigantic store of carbon which may otherwise reside in the atmosphere. Joosten and Couwenburg (2008) estimate that peatlands hold between 550 gigatonnes of carbon equivalent to 30% of all global soil carbon, 75% of all atmospheric carbon, equal to all 8


Conserving Bogs

1.4

Values and Uses of Bogs

terrestrial biomass, and twice the carbon stock in the forest biomass of the world. Worldwide, the remaining area of pristine peatland (>3 million km2) presently sequesters less than 100 Mt C yr-1 (Joosten & Couwenberg, 2008) although this rate would have been far higher before widespread damage to peatlands occurred in historic times.

1.4. BOGS AS AN EDUCATIONAL RESOURCE In an effort to inform and educate the public of the need to conserve peatlands, some conservation organisations have focused on environmental education as an integral part of their campaigns. In Britain and Ireland in the 1980s and early 1990s, Friends of the Earth, the Scottish Wildlife Trust and the Irish Peatlands Conservation Council (IPCC), Department of the Environment (Northern Ireland) and Scottish Natural Heritage all produced peatland education packs for this purpose. These packs demonstrated that bogs are a rich educational resource ranging from botany through to archaeology to poetry and painting. Indeed, the IPCC found that the value of their pack far exceeded their expectations proving to be useful in teaching environmental education at primary and secondary levels. The IPCC peatland education pack (IPCC, 1992) was split into six modules spanning science, history, geography, art, craft and design, English and Gaeilge reflecting the breadth of subjects which peatland study can offer. Another example is the Moorland Centre at Edale in the English Peak District. This Visitor Centre provides displays and information on the moorlands and peat bogs of the Peak District and the role being played by the Moors for the Future Partnership to restore upland blanket bogs. Many peat bog sites are now nature reserves which can be used for educational purposes. Some sites were specifically developed for educational purposes, e.g. Langlands Moss in Scotland and Peatlands Park in Northern Ireland. Obviously, in using peat-bogs as an educational resource, care must be taken not to significantly damage the bog and to conduct safe visits. Access facilities (see 5.6) are clearly important in this respect.

1.5 NATURE RESERVES AND WILDERNESS AREAS Peatlands can make fascinating natural and cultural reserves. They have intriguing wildlife: home to peatland specialists, a refuge for wetland species and a significant part of an area’s biodiversity. Their natural interest is complemented by archaeological finds and palaeoecological research. The two interests have been successfully combined at some reserves (for example, Shapwick Heath). This combination of factors has led to the creation of many peatland-based nature reserves. Additionally, peatlands are now so threatened that, in some countries, nature reserve designation forms the mainstay of peatland conservation programmes. In the Netherlands, for example, nearly all remnants of the once extensive Bourtangermoor are now conserved as nature reserves. Types and uses of reserves vary considerably. Peatlands Park attracts many thousands of visitors a year and is one of Northern Ireland’s most popular tourist attractions. The emphasis at the Park is on access, interpretation, education and recreation which run alongside conservation of intact bog and fen habitat. Many peatbog nature reserves have been created as wildlife havens only. These reserves are thought to be too sensitive to disturbance to breeding birds etc. and to trampling damage to allow visitor access. Some of these problems can be alleviated by provision of well planned access facilities (see 5.6). On a wider scale, where peatland is dominant in the landscape, the nature of the environment forces low intensity agricultural practises. “Wilderness” areas of Britain are mountains or peatland. These large, sparsely inhabited areas such as the Flow Country (Figure 1.2) or the peatlands of the Cairngorm Plateau have immense wildlife value. They are home to rare breeding birds such as golden plover, red-necked phalarope, red-throated diver, black-throated diver and wood sandpiper. The vast wilderness peatland areas of Scandinavia, Siberia and Canada perform the same function. An interesting parallel to northern latitude bogs are the SE Asian bogs which now contain a large proportion of the world’s Orang-utan population. 9


Conserving Bogs

1.6

Values and Uses of Bogs

Wilderness areas are very important in terms of recreation. These areas can be sustainably exploited for tourism providing a calming land of natural wonder when set against frantic urban lifestyles.

1.6 THE PEAT ARCHIVE 1.6.1 Introduction The study of the peatland archive originated with discoveries in the Swiss Lakes Region in the 1850s inspiring workers such as Arthur Bulleid who sought and found a lake village site in the Somerset Levels in 1892. In recent times, the importance and enhanced value of wet-sites over dry-sites has been realised because of more detailed studies (e.g. Godwin, 1981). As techniques develop, the archaeological value of waterlogged deposits is likely to grow so it is imperative that these records are conserved. Once lost, this rich archaeological archive cannot be restored or rehabilitated. The last few decades have seen a considerable growth in the study of wetland archaeology. This reflects both the increasing threats to wetlands and the increasing realisation that wetlands, particularly peat bogs, with their unique qualities of preservation of organic material (including the palaeoenvironmental record) can augment and very often lead to a reinterpretation of human activity in the past, particularly in prehistory (e.g. Coles & Coles 1986). Peat substrates have a low pH and are anaerobic prohibiting the activity of those microbes (bacterial and fungal) responsible for the decay of organic materials (these include wood, pollen, textiles and human bodies). Today, many archaeologists consider the palaeoenvironmental or palaeoecological record to be important in its own right and not merely as an add-on to site-based studies. Wetland sites are particularly important in that cultural evidence is within its contemporary environmental context. This can be either ‘natural’ or anthropogenic. 1.6.2 The Nature of the Resource The archaeological record preserved in wet sites should not be understated:  Extensive water-logged deposits can contain whole landscapes and conserve the palaeoenvironmental record on a regional, as well as a local level.  Wet-sites have often engulfed and preserved pre-existing land surfaces.  On a temporal level, dry-sites can occasionally, and at best, contain deposits of a few hundred years; wetsites can contain evidence over much of the Holocene and beyond.  Wetland sites preserve artefacts extraordinarily well providing information about past lives in wetland areas. This section gives a brief overview of various aspects of the archive: A Sacred Place Human activity in bogs has been varied. It has been a place to placate the deities as attested at Flag Fen (Pryor 1991) with offerings of high status goods. Less palatable today is overt human sacrifice as attested archaeologically from the Iron Age in bogs such as Lindow Moss in Cheshire (Stead, Bourke & Brothwell 1986).

10


Conserving Bogs

1.6

Values and Uses of Bogs

Fig 1.6. Lindow Man is a wonderfully preserved bog body. He lay undiscovered in a bog in Cheshire for 2000 years. (© British Museum). Prehistoric Exploitation of the Wetland Resource Fens in particular, were considered to be a rich resource in the past. "The fatness of the earth gathered together at the time of Noah's Flood" is an early 17th century description of the East Anglian fens. Such areas could be rich in food stuffs such as fish and fowl, and provide useful raw materials such as reeds and rushes. In Somerset, hunting platforms were constructed upon the mire surface as early as the Neolithic (Coles & Coles 1986). Such activity has continued through time culminating in the duck-decoy pools of the Post-Medieval period. Trackways, Communication and Access Bogs and marshes can be treacherous places; consequently people living in adjacent areas have made efforts to cross them safely since the early Neolithic period. The earliest known trackway in the UK is the Sweet Track (3807/6BC) in the Somerset Levels. To date, over 1,000 wooden trackways have been located in peat in Ireland, Britain, the Netherlands, Germany and Denmark (see Figure 1.7).

Fig 1.7. The photo shows a late Neolithic (dated to 2730-2450 BC) ‘corduroy’ trackway on Hatfield Moors under excavation (Henry Chapman). For further information see; Chapman, H.P. and Gearey, B.R. 2013. Modelling Archaeology and Palaeoenvironments in Wetlands: the hidden landscape archaeology of Hatfield and Thorne Moors. Oxbow, Oxford. 11


Conserving Bogs

1.6

Values and Uses of Bogs

Analysis of wooden artefacts and structures from peat bogs has demonstrated the highly developed skills acquired by our ancestors in terms of wood working technology and woodland management. Both areas of expertise were advanced by the early Neolithic.

Water Transport: Archaeological evidence from peat bogs demonstrates the use of boats in and around the wetlands of the past. Several examples of log boats exist from Somerset and elsewhere in Europe and North America (Figure 1.8). Prehistoric Settlement: There is little evidence to suggest that people lived within mires or marshes in the past. The majority of the settlements associated with prehistoric exploitation of wetlands took place upon the adjoining dry-lands.

Fig 1.8. A peat preserved boat (Broadland FAP) In Somerset, two exceptions to this rule are the Lake Village sites at Glastonbury and Meare. Both sites date from the Iron Age and offer an insight into life at that time. A Palaeoenvironmental Resource Examination of the peat substrate for palaeoenvironmental information includes varied analyses. The waterlogged deposits facilitate excellent preservation and a more complete palaeoenvironmental record than dry sites. The organic nature of peat facilitates radio-carbon dating which enhances the value of the deposits. Radio-carbon dates can often be supplemented and enhanced by tephra chronology and dendrochronology. Tree ring dating can achieve an impressive degree of accuracy for some timber going back to the Neolithic. For example, it is known that the Sweet Track was constructed, through a reedmarsh, in the winter of 3807-6BC (Hillam et al. 1990). Vegetational change can be detected at two levels. Macrobotanical remains (seeds, fruits, nuts, leaves etc.) indicate local and wider environmental conditions whilst pollen analysis offers more general information about vegetation change and provides evidence of the environmental (hydrological, climatic, anthropogenic) implications of such change. Wood deposits are extremely useful, not only as environmental indicators, but because wood lends itself to dendrochronology (tree ring dating) which can be accurate to the year of felling. Microfauna are usually sensitive to environmental oscillations and adapt quickly; larger animals are slower to react. The study of insect remains, in particular beetles and weevils, is particularly appropriate to peat soils as their exoskeletons survive very well in the acidic anaerobic environment of waterlogged peat. The calcium carbonate shells of land and marine molluscs can survive in some peats (pH dependent) and reflect local conditions. Bone however, rarely survives in acidic peats. Other microscopic remains examined from peat samples are Foraminifera (one celled organisms) from sediments resulting from marine transgressions and testate amoeba (unicellular algae whose siliceous walls survive). Both enhance our understanding of the environment and environmental change. The types of analyses described above can be used to build up an understanding of the past environment. This can be used to demonstrate environmental change both spatially and through time, particularly when combined with radio-carbon dates.

12


Conserving Bogs

1.7

Values and Uses of Bogs

Historic Exploitation of the Wetland Resource In many peatland areas, more modern peats were removed by the hand cutters (Figure 1.9) of the past for use as fuel or as deep litter (prior to the 1950s). The earliest known peat cutting in Somerset, for example, is from Romano-British briquetage mounds, where peat was used as fuel in the salt production process (Leech, Bell & Evans 1983). The medieval period saw efforts at wetland exploitation in such areas as the Somerset Levels (Williams 1978) where monastic influence irreversibly altered the landscape via drainage regimes. The post-medieval period witnessed the impact of the great Dutch drainage engineers in areas such as the English Fens (Hall & Coles, 1994). Exploitation of the resource has continued up to the present, more recently for horticultural purposes and in many areas very intensively. Past exploitation has largely restricted archaeological examination of peat deposits from the historic period. Nevertheless, the present landscape reflects both ancient and modern drainage systems and land tenureship. Fig 1.9 Woman carrying peat and knitting; Stornoway (© from the personal collection of Ian D. Rotherham). The Industrial Heritage: Historic exploitation and management of peatlands have resulted in the present historic and industrial landscape. The growth in the study of post-medieval and industrial archaeology places an emphasis upon landscape and architectural features previously considered to be of little value (e.g. Figure 1.10).

Fig 1.10. The old peat cutting factory at Fenn Moss has been preserved for its industrial archaeological heritage (Dr. Joan Daniels M.B.E.).

1.7 CATCHMENT HYDROLOGY

Figure 1.11 Many Scottish Rivers have their origins within peatland catchments (Niels Jelsma)

The hydrology of bogs (see 2.5) lies within the framework of the river catchment. A peat-bog’s influence may be small if it composes a small part of the catchment. Often though, bogs play an important and sometimes dominant role in catchment hydrology. The River Sebangau’s catchment in Kalimantan, for example, is wholly contained within a peat-bog. In Scotland and northern England, virtually all major rivers have their source in peat or peaty soils of the uplands (Figure 1.11). Three influences between bogs and river catchments are considered here: land-use, water chemistry and hydrology. 13


Conserving Bogs

1.8

Values and Uses of Bogs

Land-use Many extensive areas of upland bog support only low intensity landuse. Whilst the ecology of upland blanket bog (see 2.3.2) has been altered by burning and grazing, the basic functioning and ecology of these areas remains intact. Consequently, water courses coming out of these upland areas tend to be little disturbed and fairly ‘wild’-running. However, where upland bog has been heavily drained, afforested or eroded (see 1.14), water-sources are altered and downstream effects occur. For example, heavy erosion of south Pennine (UK) blanket bog has resulted in a dramatic silting up of reservoirs (see 4.5.6.2). Hydrological regimes of waters emanating from drained bogs are different from more natural watercourses. Water Chemistry Water draining from peat bogs tends to be cool, oligotrophic, acidic and contain a high concentration of organic substances (see 2.6). This is because, for deep peats, underlying mineral deposits play no part in the chemistry of surface waters. Acidity and nutrient status are, therefore, dependent upon the peat and the wet and dry atmospheric deposition of salts. Given such a low pH, storm events and acid deposition have less effect than might be found in waters emanating from non-peat catchments. Where acid-sensitive mineral soils abut peaty soils, the presence of high concentrations of organic substance in surface waters is important in counteracting the effects of ‘acid rain’ as one of the most important causes of acid-water toxicity is high concentrations of aluminium. Organic compounds form complexes with aluminium helping to ameliorate the toxic effects of acid rain. Catchment Hydrology Intact peat-bogs have a fairly ‘flashy’ water discharge regime characterised by large differences between low and high flows and a rapid rise in the hydrograph following storm events. This is because most of the peatbog is saturated. Only a thin layer (the acrotelm) is available for changes in storage (see 2.5).

1.8 PEAT EXTRACTION (See A1.2) 1.8.1 Introduction Peat is light, high in organic matter, has excellent water retention properties and is easy to cut. Given these properties, peat has been cut for many thousands of years. Peat has long been used as fuel. Hand-cut peat banks, a traditional feature of Scottish and Irish peatlands, are long established for fuel cutting (Figure 1.9). These small-scale activities contrast to the highly mechanised extraction of peat for peat-fired power stations in Ireland and Finland (Figure 1.12).

Fig 1.12. Vast wet deserts have been created where peat is commercially harvested for fuel and horticulture (Rob Stoneman). In the twentieth century, peat has also been cut commercially to provide bedding material for horses and cattle and, more recently, to provide a potting and soil substitute for professional and amateur gardening (Figure 1.13). This use has had dramatic effects on Europe's lowland peat bogs. There are four main types of cutting techniques: domestic cutting, extrusion, (sausage-cutting), sod or baulk/hollow cutting and milling.

14


Conserving Bogs

1.8

Values and Uses of Bogs

Fig 1.13. Gro bags containing peat for amateur gardening 1.8.2 Domestic Cutting This is the traditional method of cutting peat. Peat is cut out to form a bank which then proceeds forwards as peat is cut-away (Figure 1.9). The upper vegetated layer is discarded and thrown behind the working face. This has the desirable effect of re-vegetating the bare peat left behind the face hence maintaining bog vegetation and giving a firmer surface to work on. The effects of domestic cutting can be significant. As peat is removed, the size and shape of the peat body changes and so the hydrological properties of the bog (see 2.5, 2.6) alter. Water-levels fall next to the peat cutting area or may be altered across the whole bog. Widespread cutting results in an uneven surface characterised by drier heath vegetation and wetter boggy pools with occasional areas of fen where the peat has been almost completely cut-away. Mediaeval peat cutting was widespread in Britain, with many upland peatlands cut-away for fuel. Typically these cut-away areas are dominated by Nardus stricta (mat grass) and Molinia caerulae (purple moor grass). The peat banks are rarely clear on the ground but can sometimes be discerned on aerial photographs. 1.8.3 Sausage Cutting or Extrusion Traditional cutting was largely superseded by tractor driven machines which cut slits beneath the surface, extracting a 'pipe' of peat and laying it onto the surface (Figure 1.14).The 'sausages' of peat are then left to dry before being cut up as burning briquettes. Bogs, cut in this way, are effectively drained by the creation of sub-surface drainage channels whilst the peat structure is disturbed as cutting continues. Sites, cut in this way on a commercial basis, are drained and the vegetation is stripped to allow easier machine access and to stop 'sausages' becoming entangled in vegetation. Fig 1.14. Mechanised sausage cutting is now a common method of peat harvesting. Sites cut in this fashion are particularly difficult to manage as much of the active drainage is sub-sruface. This method of cutting is replacing more traditional techniques particularly in Ireland and the Scottish Highlands (Steve Wilson). 1.8.4 Baulk and Hollow (Sod) Cutting Up until the late 1980s, most commercial peat operations used a baulk and hollow pattern of cutting, initially by hand and lately by machine, to extract peat. Bogs are drained by a rectilinear sequence of drains to allow peat to be extracted from rectangular 'fields' or hollows which are bordered by drains. The blocks of cut peat are dried on intervening baulks. Baulk and hollow cutting leaves a distinctive pattern (Figure 1.15).

15


Conserving Bogs

Values and Uses of Bogs

Fig 1.15. The distinctive pattern left by peat cutting. After abandonment, the hollows often recolonise with vegetation characteristic of wet bog whilts drier areas are colonised by scrub or dry Heath (Libby).

1.9 0

1.8.5 Peat Milling Most commercial extraction operations today utilise peat milling. The first phase of a milling operation is to drain the surface layers with a series of regularly spaced deep drains. After the upper peat has dried sufficiently to allow machines to pass over, the surface vegetation is removed to create vast bare, black fields (Figure 1.16). The top layers are then rotavated (milled) to allow drying before being bulldozed into long ridges. The peat is then removed for bagging or transported directly into power stations. On cessation of extraction, the bare peat fields are inhospitable to vegetation establishment although, with careful management, wetland can be created. Without management, peat fields slowly succumb to scrub. Fig 1.16. Deserts are created on bogs stripped of vegetation, drained and mechanically harvested (ŠRSPB).

1.9 AGRICULTURE (See A1.3) Much peatland has some agricultural value, principally for light grazing. In an effort to improve grazing, there has been a long tradition of burning and drainage to dry the ground and improve the vegetation (Figure 1.17). These activities are intensified through more drainage, fertilising and seeding gradually diminishing any peatland character. At its most extreme, peat is simply cut-away to leave a thin layer which is ploughed into underlying clays to create arable land.

Fig 1.17. Many peatlands are ‘improved’ for grazing by implementing a regime of burning and drainage. This tends to produce a vegetation dominated by heather to the detriment of other typical bog species, notably Sphagnum moss (YPP).

However, in many areas bogs are used for marginal agriculture only. This causes a change in species composition although it need not be irreversible.

16


Conserving Bogs

1.10

Values and Uses of Bogs

1.10 FORESTRY (See A1.4) In continental climates, hot and dry summer weather allows trees to establish on bogs to become part of the site's natural flora. In more oceanic climates, such as Britain and Ireland, trees are very rarely a natural component of bog vegetation. However, bogs have been widely afforested as technology has allowed foresters to exploit peatland areas (Figure 1.18). Trees, often non-native species such as lodgepole pine and sitka spruce, can be established on sites through drainage and fertiliser application (Figure 1.19). As trees mature and form a closed canopy, interception of rainwater (up to 30%) acts to maintain dry enough conditions for tree growth. The afforested bog is transformed from open bogland to monotonous monocultures of non-native conifers overlying a bare, shaded surface covered with dead needles. On rides and unplanted blocks, some of the character of the former bog can remain suggesting rehabilitation is possible (see 5.3).

Fig 1.18. Many peatlands have been afforested in the last fifty years. This is a typical example of a raised bog (Carnwable Moss) that has been truncated by a railway and afforested on one side (S.G. Moore).

17


Conserving Bogs

Values and Uses of Bogs

1.11

Fig 1.19. Prior to planting extensive drainage and fertilisation is required before trees can begin to grow on deep peat. This is a view of the Flow Country in Scotland, which, in the 1980’s was the centre of a debate between conservationists and foresters (Norman Russell).

1.11. DEVELOPMENT (See A1.5) Bogs can form a barrier to development and are, therefore, modified or cut-away to allow development to take place. As with many other habitats, bog-land is lost to roads, railways, housing, industry, mining and waste disposal. Open cast mining and waste-disposal have had a particularly serious impact on Britain's lowland raised bogs whilst Britain’s upland bogs are under threat from wind farm construction. In some cases, developments are localised (such as roads) but in many cases, development leads to the outright destruction of the site.

Fig 1.20. Many lowland raised bogs have been destroyed by open cast mining and landfill operations (Chris Miller).

1.12 RECREATION (see A1.6) In some places, such as the British Isles, peatlands form important recreational landscapes supporting landscape and nature tourism that underpins local rural economies. However. Unmanaged recreational pressures can have a considerable impact through trampling and erosion. Grouse shooting in Britain 18


Conserving Bogs

1.13

Values and Uses of Bogs

has extended beyond upland heath habitats in the last few decades as state sponsored peatland drainage during the 1950s to the 1980s has degraded blanket bog. A switch from Sphagnum dominated bog to low shrub dominated vegetation (particularly Calluna vulgaris - heather) is encouraged by game keepers through regular burning.

Fig 1.21. Bogs are susceptible to damage from unmanaged access. A trackway is quickly created (YPP).

1.13 POLLUTION (see A1.7.1) The types of uses discussed above have mostly direct and fairly obvious forms of damage associated with them. However, bogs are also damaged from other less obvious sources. Particularly worrying is pollution. Pollutants can enter bog systems in different ways:  Via the atmosphere; from industrial and vehicular emissions or fertiliser drift from agriculture. As bogs receive all their inputs from the atmosphere, they are extremely nutrient deficient and hence very sensitive to atmospheric pollution. Nitrogen pollution appears to be particularly significant.  Via drains or surface run-off where drains direct water into a site from an adjacent enriched/polluted source.  Via direct application for agricultural improvement.  Via faecal enrichment from bird roosts and grazing animals or enrichment from dead animals. Some of these effects are localised but all significantly alter vegetation composition generally from oligotrophic (nutrient-poor) to mesotrophic or eutrophic (nutrient-rich) vegetation.

1.14 CUMULATIVE IMPACTS (see A1.7.2) The cumulative impacts of many differing small-scale damaging activities may be the most significant but least understood cause of peatland degradation. The relationships between flora, fauna, peat and hydrology are complex and inextricably interlinked (see 2.5); changes in one affects all the others. For example, peat removal from one side of a raised bog could eventually affect the vegetation on the other side of the bog. The time-scale over which these changes occur are unknown but may be very slow given the extremely slow movement of water in the lower saturated catotelm layer (see 2.5). As a consequence, it is sometimes quite difficult to identify the main causes of degradation to a site. It may just be the cumulative effect of centuries of small-scale damaging activities. Another form of possible degradation manifests itself as peat erosion - a widespread phenomenon on upland blanket peats (see 4.5.6). It is generally considered that no single mechanism can explain erosion of bog peat in the British Isles. Anthropogenic influences such as sheep grazing (see 1.9, A1.3.3), burning (see 1.9, A1.3.5), drainage and atmospheric pollution (see 1.13, A1.7.1) may be causative factors although some erosion may just be a natural phenomenon due to the dynamic nature and inherent instability of peatland systems (Tallis, 1985; Stevenson, 1990). For example, higher stocking rates of sheep can increase erosion and prevent eroding peat from stabilizing and becoming revegetated (Birnie & Hulme, 1990; Birnie, 1993). The two main types of erosion processes are those predominated by running water (more common) and those relating to mechanical failure and mass movement of peat. Water erosion produces linear and dendritic/reticulate channel systems depending on local topography. Linear channels generally occur on the steeper slopes and only occasionally intersect one another, whereas reticulate channels form a dense network around blocks of vegetation-capped peat. Extensive areas of bare peat are generally preceded by reticulate erosion or may result from severe fires. Although mass movements of peat occur relatively infrequently, they can have a major impact. They are characterized by slumping and/or debris flow features - bog bursts (Werrity and Ingram, 1985). Large blocks of peat, which may be several tens of metres across, 19


Conserving Bogs

1.14

Values and Uses of Bogs

become detached at the margin of peat-covered plateaux or on steep slopes, to slide or flow down-slope. This catastrophic event is triggered by major rain-storms.

20


Conserving Bogs

Distribution and Ecology

PART 2 DISTRIBUTION AND ECOLOGY This part acts as an introduction to bog ecosystems. Bogs are unusual habitats and an understanding of their ecology is key to effective conservation management. Part 2 is divided into the following sections:

2.1 CLASSIFICATION 2.2 DISTRIBUTION 2.2.1 World-wide Peatland Distribution. 2.2.2 British Peatland Distribution 2.2.3 Blanket Bog - Global and British Distribution. 2.2.4 Raised bog - British distribution. 2.3 RAISED AND BLANKET BOGS AND THEIR FORMATION 2.3.1 Raised Bogs 2.3.2 Blanket Bog 2.4 BOG VEGETATION 2.41 Introduction 2.4.2 Western Blanket Bog 2.4.3 High Level or Eastern Blanket Bog 2.4.4 Lowland Bog 2.4.5 Damaged Bogs 2.5 BOG HYDROLOGY 2.5.1 Inputs and Outputs 2.5.2 The Water Balance 2.5.3 The Hydraulic System 2.6 BOG CHEMISTRY 2.6.1 Peat Hydrochemistry 2.6.2 Peat Soil Chemistry

21


Conserving Bogs

2.1

Distribution and Ecology

2.1. CLASSIFICATION Peatlands include a rich diversity of habitats. The range and variability of these habitats is rich; classification systems reflect that diversity. Joosten & Clark (2002) provide a useful set of definitions: 

Peatlands are wetlands – areas that are inundated or saturated with water long enough for the development of vegetation communities adapted to saturated soil conditions.

Peat is an accumulated material consisting of at least 30% dead organic matter.

A peatland is an area with or without vegetation with a naturally accumulated peat layer at the surface.

A peatland where peat is actively forming is a mire.

A suo is a wetland with or without a peat layer dominated by vegetation that may form peat.

Mires are commonly then subdivided into fens and bogs (Tansley, 1939). Fens are mires which are influenced by groundwater (geogenous) whilst bogs are fed solely by precipitation (i.e. ombrogenous). However, in England this simple system becomes slightly confused as some valley fens are called bogs (for example, in the New Forest). More detailed classification schemes relate to different criteria. Moore (1984) describes seven different features which are used either separately or together to classify mires. These are: floristics, vegetation physiognomy, morphology, hydrology, stratigraphy, chemistry and peat characteristics. Of these shape (morphology), chemistry, plants (floristics) and structure are most widely used. Shape In areas where rainwater amounts are high, peat can accumulate above the groundwater level and form rain-fed mounds commonly called raised bogs. An early classification scheme was developed by Osvald (1925) who distinguished continental, Baltic, Atlantic and upland raised bogs. Baltic raised bogs are considered as classic with an outer lagg zone, a distinctive sloping rand and a gently domed cupola (Figure 2.1). Continental bogs are similar but forested. In more oceanic areas, Osvald noted that the surface of the dome was much flatter forming a plateau rather than a dome; these were distinguished as Atlantic raised bogs. Shape is also used to subdivide raised bogs into concentric (broadly symmetrical) and eccentric bogs. Most raised bogs in Britain are concentric although some Lagg g

Rand

Mire expanse

Bog

Fen deposits

Mineral deposits

Fig 2.1 Figure 2.1 Profile of classic ‘Baltic’ type raised bog. eccentric bogs do exist, e.g. Claish and Kentra Mosses, Argyll). Raised bogs are usually limited in extent and have a recognisable boundary (the rand).

22


Conserving Bogs

2.1

Distribution and Ecology

Upland raised bogs are now not regarded as raised because they are unconfined, i.e. have no recognisable rand. In predominantly upland areas where rainwater levels are so high that the ground remains wet enough for peat-forming species to establish the peat is capable of overwhelming whole landscapes to create a blanket of peat of varying depths. These unconfined peatlands are termed blanket bog (Gore, 1983). Chemistry The broad subdivision between bog and fen is reflected chemically as fens are usually more eutrophic because of the nutrients within groundwater; nutrient levels are in turn affected by ground conditions which are very variable. Bogs are nutrient-poor because they are rain-fed. However, the amount of nutrients coming into a bog relates to the quantity of rainfall and distance from the sea. Sea-spray onto bog surfaces increases the nutrient status of a bog whilst high rainfall serves to increase the total amount of nutrients falling onto a bog. These chemical variations partly account for a distinct east-west differentiation of blanket bogs in the British and Irish Isles (Ratcliffe, 1977). Plants A valuable approach to mire classification is based on floral composition (Moore, 1984). Classifying mires on a botanical basis alone has been extensively used in Central Europe (e.g. Rybnicek, 1984). In the UK the National Vegetation Classification (Rodwell, 1991) classifies mires into 38 different types, each of which are further subdivided. Whilst other NVC types may be found within bog habitat, the main bog vegetation communities are represented by seven NVC types: M1 Sphagnum auriculatum bog pool community, M2 Sphagnum cuspidatum/recurvum bog pool, M3 Eriophorum angustifolium bog pool community, M17 Scirpus cespitosus - Eriophorum vaginatum blanket mire, M18 Erica tetralix - Sphagnum papillosum raised and blanket mire, M19 Calluna vulgaris - Eriophorum vaginatum blanket mire, and M20 Eriophorum vaginatum blanket and raised mire. However, the NVC may be too coarse as a classification system for mires with others (Lindsay, 2010) suggesting that the CORINNE or EUNIS phytosociological classification systems are more appropriate to mires. Structure A different way of classifying bogs is to consider active structural or morphometric units. Ivanov (1981) suggested a 4-stage bog classification scheme: (i) mire microform such as a hummock or hollow; (ii) mire microtope - a group of microforms making up a surface patterning on a bog; (iii) mire mesotope - a body of peat which makes up a single hydrological unit such as a raised bog; and (iv) mire macrotope which relates to situations where mesotopes have coalesced. Lindsay et al. (1985) describe a series of labelled structural components which can be used to assess the hydrological condition of a bog (Figure 2.2). Macrotope – hydrologically linked fens and bogs within a landscape bounded by non-peat forming landscape features. Mesotope – individual, identifiable peatland units Microtope – the surface pattern e.g. hummock-hollow. Nanotope – the individual elements of the surface pattern e.g. hummock or low-ridge. The National Peatlands Resource Inventory (NPRI) represented a first attempt to map and classify all of Great Britain's peat deposits. Since then there have been no systematic surveys focused on mapping the extent and condition of peatlands across the UK, although in 2011 a review of a wide range of different datasets was carried out in order to provide a more comprehensive assessment of the state of UK peatlands (JNCC, 2011). 23


Conserving Bogs

Distribution and Ecology

2.2

Fig 2.2 Generalised distribution of microforms and an idealised distribution of species found on Northern British bogs (adapted from Lindsay et. al., 1988).

2.2 DISTRIBUTION 2.2.1 World-wide Peatland Distribution. On a world-wide scale, mires cover an extensive area. Problems with definition and mapping make it difficult to give a precise figure although estimates suggest there are around 4 million square kilometres (Joosten & Clark, 2002) - about the size of India and Pakistan or 3% of the world's land surface. Figure 1.2 shows the global distribution of mire. The northern boreal countries have the highest concentrations of mire: principally Canada, USA, Russia, Finland, China, Sweden and Norway. Huge areas of peatland are also found in the tropics: principally in Indonesia and Malaysia. 2.2.2 UK Peatland Distribution

The UK’s mires show considerable diversity. Taylor (1983) gives examples of valley mires, schwingmoors, raised bogs, upland blanket bog, lowland blanket bog and basin mires. A variety of factors (including high oceanicity; the existence of high altitude peneplanation surfaces; glacial history; Holocene sea-level rise; and the impact of human culture at a time of deteriorating climates) have conspired to give rise to somewhere between 7.4% and 9.7% of the UK's land surface being covered with mire (though rather dependent on classification and typification – figures based on JNCC, 2011). The greatest areas of peat development are in the north-west reflecting a highly oceanic climate. The relatively more continental climate of the south-east is less favourable to peat development. In this handbook, the focus of restoration techniques is firmly on UK bogland – our raised and blanket bogs. Fen restoration is comprehensively dealt with through the Fen Management Handbook (SNH, 2011) Of the UK bogs, there are clear differences between north-western or upland blanket peats and predominantly lowland raised bogs in terms of their setting, shape, flora and fauna (see 2.1). Figure 2.3 shows the current distribution of blanket, raised and intermediate bog as classified by JNCC (2011). Today, many of the historic lowland bogs have been severely modified and are now unrecognisable as peatland ecosystems, i.e. they are afforested or used as pasture or arable land.

24


Conserving Bogs

Distribution and Ecology

2.2

Fig. 2.3 Peat and peaty soils of the United Kingdom (JNCC 2011). The map shows clearly that raised and intermediate bogs are a restricted habitat in UK. In sharp contrast, blanket bog is the dominant habitat in large areas of the country, especially in the uplands and the north and north-west. 2.2.3 Blanket Bog - Global and British Distribution. The predominance of blanket bog over large areas of the UK is globally unique. Formation of blanket peat requires a climate which is both wet and cool. Indeed, rather exacting climatic conditions are required for blanket bog formation. Lindsay et al. (1988) point to a combination of a minimum annual rainfall of 1,000 mm, a minimum of 160 wet days and a cool climate (mean temperature below 15oC for the warmest month) for blanket peat formation. Superimposed on this climatic pattern is the role of human cultures in initiating 25


Conserving Bogs

2.2

Distribution and Ecology

blanket peat development (Moore, 1973). Lindsay et al. (1988) indicates parts of the globe where climatic conditions appear to be suitable and those where blanket bog has been recorded (Figure 2.4).

Fig 2.4 The global distribution of blanket mire. Blacked areas represent regions where blanket bog has been recorded (adapted from Lindsay et. al, 1998).

The diagram clearly shows that on a global scale, blanket bog is a very limited resource. Lindsay et al. (1988) tentatively estimates a total global resource of about 1.3 million ha of which 13% is found in Britain. The UK and Ireland are considered as the classic region for blanket bog development. Arguably the finest area of blanket bog in the UK occurs in Caithness and Sutherland - the Flow Country (see Figure 1.2). A combination of an extremely oceanic climate and a fairly level topography has resulted in 4,000km2 of almost continuous blanket bog. Ratcliffe and Osvald (1987) sum up its international significance:  it is the largest and most intact known area of blanket bog in the world;  it is a tundra-like ecosystem in a relatively southern region;  it has developed unusually diverse systems of patterning;  it has a unique floristic composition;  it has a tundra-type breeding bird assemblage;  it has significant fractions of notable bird species; and  it has insular ecological adaptations by several bird species which may represent incipient evolutionary divergence in Britain.

26


Conserving Bogs

2.3

Distribution and Ecology

2.2.4 Raised bog - British distribution. In contrast to blanket bog, "classic" or "type-site" raised bogs are the Hochmoor (literally translated as high moor) raised bog of the Baltic region (see 2.1). In Britain, the dome of peat is less pronounced with cupolas which are often flat. The margins of bogs are often less sloped, grading gently down to the mineral soil. In addition, lagg fen systems are rarely found mostly due to drainage of lagg fen systems for agriculture (see 1.9, A1.3). Raised bogs are generally found in the lowlands, exist as discrete peatland units in a non-peat landscape, are raised above the general land surface and have a surface topography which is mostly independent of sub-surface topography. Raised bogs are largely found to the north and west of England, and the lowlands of Scotland. A few raised bogs are also found in Wales with outliers in east and south-west England. The original resource, shown in Figure 2.3, has now been severely depleted through conversion to agriculture, afforestation and more recently peat extraction for horticulture (see 1.8 -1.14). Today, raised bogs, which are still dominated by "near-natural" flora, are found mainly in central Scotland with a few other examples around the Solway Firth and in Wales. Twenty per cent of the whole British resource of raised bog is found in the Upper Forth carselands. Here, eighteen raised bogs exist of which six are SSSIs and one - East Flanders Moss - represents the largest expanse of "intact" raised bog in Scotland.

2.3 RAISED AND BLANKET BOGS AND THEIR FORMATION 2.3.1 Raised Bogs Raised bogs often develop over shallow basins formed during the last Ice Age. After the ice retreated from northern parts of Europe, the landscape was littered with many depressions within a mantle of often impermeable glacial debris or till. These basins formed lakes and were colonised by a fringe of fen vegetation. In-washed material formed lake sediments which when mixed with dead and undecayed plant material eventually led to many lakes completely infilling. Classically, it was thought that this sequence of succession gradually led to the development of forest over the former lake (e.g. Tansley, 1939). Walker (1970), however, showed that this sequence of succession is rare. Instead, as the lake basin is filled with fen peats and sediment, the plants at the centre are cut off from nutrients at the lake margins making conditions rather nutrient poor. Sphagnum bog mosses thrive in nutrient poor and waterlogged conditions such as these and can dominate in these situations (see Figure 2.5). Sphagnum leaves are characterised by large and empty hyaline cells sandwiching much smaller photosynthetic cells. The hyaline cells act as water conducting systems, to allow Sphagnum spp. to cope with waterlogging, and create a large surface area for cation exchange (Daniels and Eddy, 1990). Cation exchange is the mechanism by which Sphagnum (and other plants) absorbs nutrients dissolved in water. Sphagnum's unusual physiognomy means that the genus has a high cation exchange ability, swapping scarce

27


Conserving Bogs

Distribution and Ecology

2.3

Fig 2.5 Hydroseral succession leading to the development of a raised bog.

nutrients for hydrogen ions. As a result, Sphagnum species gradually acidify their surroundings (Clymo 1963). High acidity favours Sphagnum over many other species further allowing Sphagna to dominate the infilled former lake. Sphagna grow from the top of the plant - the apices - and die at the base. As a result, dead organic material is left in a waterlogged zone to form peat; Sphagna are efficient peat formers. Water can move only very slowly through the peat as it has a low hydraulic conductivity (Ingram, 1982). In effect, it is difficult for rainfall to leave the site and waterlogged conditions are maintained. The stage is now set for a dome of peat to form above the former lake-level and away from the influence of ground-water. Sphagnum growth continues in conditions of low nutrients, high acidity and waterlogging to accumulate layers of peat which rise above the landscape. Once a half metre layer has formed above the former lake-level, the surface becomes isolated from groundwater (Granlund, 1932). The bog now becomes dependent upon rainwater alone, i.e. the system becomes ombrotrophic (rain-fed). Rain-fed bogs derive all their nourishment from the atmosphere; bogs are highly nutrient deficient systems. 2.3.2 Blanket Bog In cool, moist and mild airstreams, ground can become so waterlogged that dead vegetation cannot decompose fully leading to the formation of peat directly onto mineral surfaces (paludification). This process is dramatically illustrated in north-west Scotland where peat forms directly upon large, isolated glacial erratics - bogs on rocks (Figure 2.6). More typically, this process - paludification - proceeds upon highly podzolised glacial tills. Constant precipitation allied to low evaporation rates leads to podzol 28


Conserving Bogs

2.3

Distribution and Ecology

formation eventually forming an iron-pan. Once an iron-pan forms, the soil above is prone to waterlogging to form a peaty-gleyed podzol. Decay processes are often slowed enough to form peat. After this stage, the peat itself holds water back because of low hydraulic conductivity allowing layer upon layer of peat to build to a considerable thickness, eventually blanketing the landscape. In Britain and Ireland, there is evidence to suggest that podzolisation and the eventual development of blanket peat was partly or, possibly, wholly the result of human intervention (Moore, 1973). Under the warmer and drier climatic conditions of the early Holocene (9000-6000 years BP), deciduous forest (across most of Britain) or pine forest (in northern Scotland) developed to cover most of the landscape. An exception may be the Northern Isles and parts of northern Scotland. Following deforestation by prehistoric farmers and an accompanying deterioration of climatic conditions in the mid to late Holocene (between 5,000 and 2,000 years BP), Fig 2.6 A peat mound growing on an isolated exposed brown earth soils, which had developed boulder – an extreme example of blanket peat under a forest canopy, became podzolised formation. eventually leading to peat formation. Whether climatic conditions would have led to forest decline and peat formation directly, without human intervention, is open to debate. Certainly, in the Flow Country, pine forest had developed on peat surfaces but eventually succumbed to wetter climatic conditions irrespective of human landuse (Charman, 1994). Once peat forms, the same set of processes described for raised bogs (see 2.3.1) operates on blanket bogs. Sphagna acidify the environment and efficiently form peat whilst peat formation itself maintains waterlogging. The surface eventually becomes rain-fed, and takes on the bog characteristics of high acidity, low nutrient status and waterlogging. Such peat formation can proceed on even quite steep slopes given appropriate climatic conditions. In the north-west Highlands, peat forms on slopes as steep as 35 (Lindsay, 1995). The distribution of blanket bog is clearly controlled by climate. In addition to paludification, other processes of mire formation can occur in blanket bog landscapes. Terrestrialisation of open water bodies via hydroseral succession to bog - usually raised bog - leads to domed, apparently raised bog units within a blanket bog landscape. Additionally, water courses are enveloped in fen vegetation and fen peats form. Blanket bog, in fact, is rather a misnomer as the landscape is often composed of a mixture of ombrotrophic (bog) and rheotrophic (fen) units (Figure 2.7). A more accurate expression is blanket mire as this includes all peatland elements. In this volume, the term blanket bog is retained for familiarity purposes. However, it should be recognised that blanket bog is actually a highly diverse landscape.

29


Conserving Bogs

Distribution and Ecology

2.4

Figure 2.7 Blanket bog landscape features (adapted from Lindsay, 1995) The diversity of blanket bog landscapes is reflected by their hydrology. Lindsay et al (1988) recognise the importance of morphology in controlling the hydrology of blanket peats by classifying mesotopes (mire units) according to their hydromorphology (see 2.1). Broad categories include: Watershed bog Saddle bog

Valleyside peats

Spur bogs Ladder fens

Minerotrophic fens

Truly ombrotrophic peats develop on the top of hills. These may have developed from terrestrialisation of pools within saddles. Saddle bogs are partly rheotrophic as they receive water from surrounding hillsides. These peats are often thin, depending upon the angle of slope. Vegetation reflects higher rates of flushing and is generally less ‘ombrotrophic’ with a lower cover of Sphagnum mosses. These combine features of saddle and valley side bogs. A special category of mire found in the Flow Country, which has affinities to ribbed fens found in Eastern Canada (Charman 1993). These form in water collection areas.

2.4 BOG VEGETATION 2.4.1 Introduction The conditions of high acidity, low nutrient status and waterlogging lead to a distinctive vegetation type. Commonly found vegetation include Sphagnum bog mosses, sedges (cotton grass and deer sedge in particular) and various heathers. The nutrient-poor conditions are exemplified by sundews and butterworts which gain extra nutrients (particularly nitrogen) by catching and absorbing insects.

30


Conserving Bogs

2.4

Distribution and Ecology

On a European continental scale, the range of vegetation types across bogs is, unsurprisingly, large. Eastern, continental bogs are tree-covered. In southern Germany, mountain pine (Pinus mugo) grows as a low spreading prostrate shrub. In more continental climates, such as Siberia, trees dominate bogs entirely. In Western Europe, a transition from the south to the north is noticeable. In Britain, vegetation variation relates mainly to east-west rainfall variation (hyper-oceanic to oceanic climates) and to altitude. Good descriptions of bog vegetation types can be found in Rodwell (1991) and McVean and Ratcliffe (1962). Four broad categories of bog vegetation are commonly encountered in the UK: western blanket bog, eastern and high level blanket bog, lowland bog and damaged bog. 2.4.2 Western Blanket Bog Western blanket bog occurs in very wet (hyper-oceanic) parts of the UK (over 2,000 mm per year and over 200 wet days per year) although it is generally found below 500 m where frost is infrequent. From a distance, deer grass and purple moor grass appear dominant. On closer inspection, the ground layer is rich in bryophytes, particularly Sphagnum papillosum and S. capillifolium whilst hare’s tail cotton grass, heathers (ling heather and cross-leaved heath especially) and, sometimes, bog myrtle are common. Wetter areas in these communities are represented by a high percentage of Sphagnum species, common cotton grass and bog asphodel. The wettest parts have bog pools which are colonised by white-beaked sedge and Sphagnum auriculatum. The driest areas may have an increased abundance of Racomitrium langinosum and Cladonia spp. The most western blanket bogs differ by the presence of black bog rush, common in western Ireland and on the Scottish island of Islay. 2.4.3 High Level or Eastern Blanket Bog At higher altitudes or in eastern areas, where rainfall is between 1,200 to 2,000 mm p.a. with 160-200 wet days per year, blanket bog vegetation is characterised principally by hare’s tail cotton grass and ling heather. This type of vegetation is prevalent across the Scottish Eastern Highlands and Southern Uplands and the English Pennines. Under a regime of burning and grazing with high levels of atmospheric pollution, hare’s tail cotton grass becomes dominant. Indeed, in the southern Pennines, heather is lost almost completely. On high areas, mountain shrubs occur like cranberry, cowberry, northern (bog) bilberry, small crowberry, bearberry, dwarf birch and the herb, cloudberry. 2.4.4 Lowland Bog In the less oceanic lowlands of NW Europe, bog vegetation is characterised by a multi-coloured carpet of Sphagnum mosses; in particular, S.magellanicum, S.papillosum, S.capillifolium, S.tenellum, S.cuspidatum and, sometimes, S.imbricatum, S.fuscum and S.pulchrum. In the mix of mosses, vascular plants such as hare’s tail cotton grass, common cotton grass, ling heather and cross-leaved heath are common with bog rosemary, bog asphodel, deer grass, cranberry and round-leaved sundew all commonly found. Wetter areas are characterised by pools of S.cuspidatum and S.recurvum. This lowland bog vegetation type is most frequently found on raised bogs although it can be found on intermediate bogs and where blanket bog extend over saddles and deep depressions (see 2.3.2). 2.4.5 Damaged Bogs Though commonly found, this type is more rarely described. Unfortunately, land managers are probably more familiar with various types of damaged bogs than the relatively pristine communities described above. Appendix 3 describes the ecological effects of various types of damage and the types of vegetation likely to be encountered. Broadly, though, the main changes relate to changes in water-level, from drainage, abstraction, peat cutting etc., and chemical conditions, from eutrophication, atmospheric pollution, burning, grazing etc. On pristine bogs, the water-level is high - only centimetres below the surface. Only in very dry weather do water-levels drop below 10-20cm. On damaged bogs, water-levels are often lower and vegetation communities are typified by heath and woodland. Particularly common is a decline in Sphagnum mosses and an increase in heathers and/or sedges. This is followed or accompanied by scrub invasion by pine or birch. Many very dried-out or cut-over bogs are now colonised by open canopy birch or pine woodland (see 31


Conserving Bogs

2.5

Distribution and Ecology

Figure 2.8). Another common element in today’s modified bogs is rhododendron. This common exotic can establish itself on wet bogs. Rhododendron thrives on drained bogs, spreading rapidly to become a monotonous dense thicket.

Figure 2.8 Effects of lowering the water table on vegetation. With lowered water table, the peat surface will also subside and shrink. Not shown in this graph for simplicity; reproduction with kind permission of Lindsay (2010). The effects of eutrophication are less clear. Direct eutrophication from contaminated waters is unusual unless the bog has been cut or waters are deliberately pumped onto the surface (see, for example 6.4). The deposition of atmospheric pollutants has been a major driver of change in UK blanket mires since the Industrial Revolution. As sulphur emissions rose through the 20th century, acid deposition the southern Pennines was a major cause of ecological damage, in particular the loss of peat-forming Sphagnum spp., and may be a contributory factor in the onset of gully erosion across this region (Tallis, 1987). Although sulphur emissions have declined by around 90% since the 1970s (RoTAP, 2012), peatlands have been slow to recover. Deposition of nitrogen compounds, which has increased since the mid-20th century and remains above the ‘critical load’ (the threshold above which damage is expected) for 40% of all bog habitat in the UK (van der Waal, et al, 2011), has the potential to trigger species change through their role as a nutrient. Excess nitrogen may cause species changes displacing Sphagnum spp. with species more suited to high nitrogen levels (Berendse, et al., 2001; Sheppard et al., 2011) leading to cessation of peat formation and potential release of CO2. In Scotland, many lowland bogs are devoid of S.magellanicum although S.fallax is abundant. This appears to be especially so near roads, suggesting atmospheric pollution may be an important factor. In central Europe, Twenhoven (1992) has found a similar replacement of S. magellanicum by S. fallax and he also postulates atmospheric pollution as the cause (A3.7.1).

2.5 BOG HYDROLOGY A key feature of active peat bogs which has a profound impact on their hydrology is the structure created by Sphagnum mosses in particular. These form a carpet with densely packed heads (capitula) at the surface and a relatively open matrix of branches and stems below this. Water can move easily through this layer. Further down the profile, however, branches and stems become more chaotic, collapse and break and become more and more tightly packed restricting both vertical and horizontal movement of water. Eventually a point is reached where the tightly packed leaves and broken stems form a brown amorphous layer of varying depth which we call peat. The open structured vegetation layer is called the acrotelm while the brown peat layer is called the catotelm and this diplotelmic model is fundamental to the understanding of raised and blanket bog hydrology. Water movement in the catotelm is highly restricted – once there it 32


Conserving Bogs

2.5

Distribution and Ecology

stays there which is why peat in a natural state remains waterlogged with little fluctuation in the water table of the catotelm The water table in the more open-structure acrotelm is more variable and it is in this layer where much of the water flow through the bog system occurs (Holden & Burt, 2002). 2.5.1 Inputs and Outputs For both raised and blanket bogs, the only water which reaches the surface comes from above as rain, snow or fog entering the bog as meteoric water. In some high altitude areas blanket bogs can be shrouded in mist for two-thirds of the year (Goudie & Brunsden, 1994) and condensation form this mist may therefore be as significant as rainfall in providing water to the bogs. Most of this water will flow laterally through the acrotelm layer although a small amount will seep vertically into the catotelm below to replace any losses that do occur. Water is lost from the system via a number of routes; Evapotranspiration: Rainwater can be caught by vegetation and is simply evaporated straight back into the atmosphere. Rainwater that is not evaporated falls onto and infiltrates into the bog surface with some of it even seeping into the catotelm. Another part of the water is taken up by plants to be returned to the atmosphere via transpiration. The total effect is termed evapotranspiration, a process that occurs readily on warm, sunny or windy days. In an intact bog the acrotelm protects the catotelm from the drying effects of evapotranspiration. The increased mist, fog and cloud cover at high altitudes will also have the effect of reducing evapotranspiration from blanket bog systems. Seepage through the matrix: In a well-hydrated bog, water occupies pores between plant material, within Sphagnum hyaline cells and between soil particles. The water within the pores can move as long as it has the energy to do so, i.e. has hydraulic potential. This potential is fired by gravity. Not surprisingly, on raised bogs, water moves downhill from the centre to the edges of the peat dome. On blanket bogs water will move down the slope and will obviously be able to move at a greater rate on steeper slopes. The rate at which it moves partly depends upon the ability of the water to move through the pore spaces. If the pores are small or the number of channels few (as in the majority of the catotelm) hydraulic conductivity is lower. As a result the majority of seepage will be in the more open acrotelm and only a small amount will enter the tightly packed catotelm. Flow within macropores and natural “pipes�: Many upland peatlands contain macropores or peat pipes of varying sizes which run through the catotelm and often connect the surface with the deeper layers. Water flow through these macropores can be rapid and turbulent and may make a significant contribution to the flow of water through blanket peat systems. Infiltration-excess overland flow: Only a proportion of the rain that falls onto a peat bog seeps into the bog itself. Where rainfall intensity is higher than the infiltration rate excess water leaves the bog as overland flow having never entered the peat. Saturation-excess overland flow: Lower intensity of rainfall over longer periods leads to saturation of the peat and excess water will find its way out of the peatland and drain downstream overland and combine with fresh rainfall that has not entered the peat. 2.5.2 The Water Balance The various inputs and outputs can be expressed by the water balance equation. Essentially, the amount of precipitation must equal the amount lost by evapotranspiration, lateral flow and vertical seepage, balanced 33


Conserving Bogs

2.6

Distribution and Ecology

by any change in the total volume of water stored in the bog itself. This is more commonly written as the water balance equation: P - E - U - G - W = 0 where P = precipitation, E = evapotranspiration, U = lateral flow (including overland flow and macropore flow), G = vertical seepage and W = the change in storage. Of these variables, vertical seepage is usually low as peat-bogs often sit on impermeable bases - glacial clays or saturated sediments - whilst for undamaged bogs, storage changes are also small as the bog is usually saturated. Evapotranspiration and lateral flow are, therefore, probably the most important ways in which a bog balances the precipitation coming in. Holden & Burt (2002) showed that for blanket bog systems the majority of the lateral flow was through saturation-excess overland flow with very little contribution from infiltration-excess overland flow. Flow through macropores was also significant contributing an average of 10% to streamflow. Given the importance of lateral seepage on raised bogs it is useful to consider how it varies across the bog. The centre of the bog receives water from precipitation alone (Figure 2.9,i). The peat around this central portion receives water from precipitation and from seepage emanating from the central area (Figure 2.9,ii). Moving outwards, each successive ring, away from the centre, receives progressively more and more water. To disperse these increasing volumes of water, the slope of water-table increases, i.e. the water in the bog must take the form of a dome - a groundwater mound (Figure 2.9,iii) or to put it another way: “A raised mire is sustained by .. discharge, which creates a groundwater mound in the catotelm, whose hydrodynamics mould the profile of the intact peat deposit to a hemi-ellipse”. (Ingram, 1992). The groundwater mound can be modelled although the equations are complex. Most important though, is that alteration of one part of the dome must affect the rest of the system. The whole peat body constitutes a single hydrological system unified by the lateral seepage of water.

2.6 BOG CHEMISTRY 2.6.1 Peat Hydrochemistry Peat chemistry is generally dictated by peatland vegetation and the influence of their microbial communities. It is also strongly influenced by human activities. Peat chemistry influences human agricultural and forestry activities and also has a bearing on water quality. This can be very important; in Scotland, for example, 95% of the country’s drinking water is derived from peatlandrich catchments. In peatlands, the process of humification produces organic acids as end-products. These organic acids neutralise incoming alkaline anions1 such as bicarbonates (the only relatively strong base

Figure 2.9 The variation of lateral seepage in successive rings around the central core of a bog.

1

Molecules are usually composed of two parts: a positively charged cation which is attracted to a negatively charged anion

34


Conserving Bogs

2.6

Distribution and Ecology

found in natural surface waters) and, therefore, become the dominant anions in peat hydrochemistry alongside hydrogen and sodium cations with smaller contributions from magnesium, potassium and calcium. Sulphate usually forms the major inorganic anion; arising from the oxidation of organic matter containing sulphur, e.g. amino acids. However, since the Industrial Revolution, much sulphate derives from human activities, e.g. as acid rain from power stations. In all cases, soluble organic matter is the dominant anion although in oceanic bogs, sodium and chloride are evident because of marine salt inputs in rainwater. The soluble organic matter gives rise to drainage water pH values of around 4.2 - 4.4 in ombrotrophic peatlands (very acidic). Drainage waters from undisturbed peatlands are usually moderately coloured but rich in dissolved organic matter. Disturbance, by erosion or cultivation or burning of the surface for example, leads to increased suspended sediment, i.e. particulate peat, and also to deeply-coloured drainage waters which can contain elevated levels of organic matter. 2.6.2 Peat Soil Chemistry The dominant components of peat are water (mainly) and humic substances. These humic substances are mostly mixtures of plant and microbial derived macromolecules formed from building blocks of polysaccharides, lignin and polypeptides. Some humic substances are water-soluble. Others are insoluble polycarboxylic acids (fulvic & humic acids) which form a variety of molecules. Some of these molecules react with calcium, thereby removing bony structures from animal remains buried in peat, and also react with substances such as skin and hair causing a tanning process which helps to preserve these. Peat also contains waxy residues (up to 40% dry weight). The high wax content makes it difficult to rewet dried peat. The macromolecules are prone to oxidation, when exposed to air, releasing nitrogen (usually as ammonium), sulphate and carbon into drainage waters from disturbed peatlands, e.g. where ditches have been dug or where the bog has been cut-away. The carbon output is usually in the form of colloidal humic substances. One of the down-stream effects of such runoff is the precipitation of dark-coloured surface coatings on stream bed sediments, especially where bog drainage mixes with calcium- and iron-rich (due to liming) runoff from improved land. This can be confused with visibly similar iron ochre deposition which may have equally-severe effects on streambed ecology.

35


Conserving Bogs

Planning Conservation Management

PART 3 PLANNING CONSERVATION MANAGEMENT The various planning stages are outlined in the following sections: DEVISING A MANAGEMENT PLAN 3.1. DESCRIPTION 3.1.1 Introduction 3.1.2 Vegetation 3.1.3 Hydrology 3.1.4 Topography 3.1.5 Special Interest - Fauna and Flora 3.1.6 Safety and Hazards 3.1.7 Archaeological, Palaeoecological and Historical interest 3.2 EVALUATION AND SETTING OBJECTIVES 3.3. ACTION PLAN (PRESCRIPTIONS), DAMAGING IMPACTS AND SOLUTIONS 3.3.1 Introduction 3.3.2 Peat Extraction 3.3.3 Agriculture 3.3.4 Drainage 3.3.5 Afforestation 3.3.6 Other Types of Damage 3.4. REPORTING, MONITORING AND EVALUATION 3.4.1 Introduction 3.4.2 Reporting 3.4.3 Survey and Monitoring 3.4.4 Evaluation and Updating

36


Conserving Bogs

Planning Conservation Management

DEVISING A MANAGEMENT PLAN This part of the Handbook discusses the management planning process and how it could be applied to bogs. On intact sites, the objectives for management are simple - to maintain the natural functioning of the bog; it may be that a ‘do nothing’ plan is all that is required. Almost all bogs are damaged and conservation management is usually required. In an ideal situation where a site is under a reasonable level of control by the conservation manager the most effective way to pursue such management is to first devise a plan (even if a do-nothing policy is the outcome). One of the most effective management planning systems is that developed by the Countryside Management System (CMS) consortium (Alexander, 2010) A good quality management plan should be set out as follows: 1. Plan Summary 2. Legislation & Policy 3. Description

4. Evaluation 5. Factors 6. Objectives 7. Action Plan

8. Monitoring & Review

Provides a rapid and clear overview of the entire site. All management plans should be written in the context of all the legislation and policies relevant to the site. The description acts as a baseline summary of what is present on the site and all the background information needed to make decisions on management of the site. The next stage is an evaluation of the site to identify it’s important features. What are the important influences on the features of the site. This sets out what it is that management of the site intends to achieve. For each objective, projects (tasks) which would achieve that objective are identified. These are then used to develop work plans or programmes. Monitoring is an essential, though often neglected, part of the management planning process. Evaluation of the successes and failures of the management plan is vital if the site manager is to update and refine the management of the site.

Good management planning is in reality a cyclical continuum allowing the plan to be reviewed annually and updated every five years to ensure that it remains relevant. Monitoring and survey is essential to monitor the effectiveness of the plan and management works. At best, each management project would have a monitoring project attached to it. In practice, this is often far too time-consuming. However, monitoring is required to evaluate whether original objectives of the plan are being realised. Management plan preparation can be a lengthy and time-consuming process. To avoid, getting tangled up in management planning at the expense of actual conservation management, begin with short and simple plans which can be expanded, if necessary, at a later date. For small and uncomplicated sites, plans need only be small - a couple of pages. This can then be built upon to form more detailed documents when plans are reviewed annually or overhauled. In many cases, sites may be in the ownership of private landowners whose objectives may not be exclusively conservation management. In addition, conservation management may be responding to short-term funding 37


Conserving Bogs

3.1

Planning Conservation Management

opportunities (1-3 years) which may not allow for detailed management planning. In some instances it may be that these sites have management plans with different levels of detail. For example, blanket bog sites in England that are managed under a Higher Level Stewardship Scheme will have some survey data obtained from the initial baseline Farm Environment Plan and will have an outline management plan as part of the agreement but this is unlikely to be at the level of a full management plan. The Yorkshire Peat Partnership works on blanket bogs in these circumstances and, out of necessity, has developed a rapid Restoration Plan approach which is designed to obtain sufficient information to enable restoration work to take place and contains elements of the management plan process described above but lacks the detail required for a good quality long-term management plan. The following sections go through the planning stages outlined above to indicate the methods and techniques which may be used to formulate an effective full management plan and monitor progress together with those used by the Yorkshire Peat Partnership to develop their less detailed Restoration Plans. The techniques used are described in more detail in Parts 4 and 5 of this guide.

3.1. DESCRIPTION 3.1.1. INTRODUCTION The description of the site is usually a collation process of known information on which the evaluation exercise can be based. This process allows short-falls within the data to be identified and gaps made up through appropriate survey. However, for bogs, management can be ineffective without an adequate baseline dataset. The complexities of bog management require various types of data. For example, a knowledge of hydrology, peat depth, underlying geology, topography, water chemistry and type of peat would all have to be gathered if the restoration of a commercial peat extraction site was considered. Vegetation, hydrology, topography and safety/hazards information is all important for effective management planning. However, a high level of detail is not always required; plan preparation or actual management need not be held up by a complex, expensive and time-consuming data collection exercise. It is clear that base-line data collection is often a map-based exercise. Geographical Information Systems (GIS) are now the tool of choice for most site managers as they enable quick and easy data manipulation. As importantly, maps concerning various aspects of site management can fairly easily be generated and there are a wide range of readily available datasets that can be downloaded free or at low cost (for example, contour data, site designations, watercourse information).

3.1.2. VEGETATION Bog management often relates to setting up appropriate conditions to maintain or encourage various types of vegetation. A vegetation map is, therefore, central to decision making. A practical way to describe the vegetation of a site is to divide it into compartments of fairly homogenous vegetation types. Compartments can be defined by three methods: 1. On small sites, walking around the site with a map may be all that is required. On more damaged sites, man-made features such as walls, fences, tracks, drains, forest boundaries, peat-cuts etc. can be used as the boundary between compartments. If there are few features on the ground for adequate orientation, a grid system may need to be installed. 2. For larger sites, it may be impractical to walk round the whole site for mapping purposes. In these cases aerial photographs should be purchased or borrowed. Interpretation of these images can then be used for initial mapping. Aerial photograph interpretation (API) of bogs should always be backed up with ground truthing since contrasting vegetation types may be indistinguishable on the photograph (see 4.6.6.1). 3. Very large areas of blanket bog are much more difficult to compartmentalise. One method, used by Scottish Natural Heritage to map blanket bog (although for inventory rather than management purposes), 38


Conserving Bogs

3.1

Planning Conservation Management

is the use of satellite imagery. Blocks of image pixels with a similar frequency (colour) are checked in the field to provide a classification system which can then be applied to the whole image (see 4.6.6). 4. The Yorkshire Peat Partnership works on heavily degraded peatlands and initially compartmentalises its sites simply into peat or non-peat based on physical parameters seen fromn aerial photgraphs (grips, peat gullies, bare peat). This is then ground-truthed in the field at a later stage. The detail to which a site may be compartmentalised depends both on the likely management of the site and available resources. A sensible mapping policy would be to compartmentalise areas of broader vegetation communities. Note that, U.K. National Vegetation Classification (NVC) mire communities are not necessarily the best way of compartmentalising a site for management purposes. Once a site is compartmentalised, vegetation information can be collected from each compartment. As ever, the amount of vegetation survey is dependent upon time and expertise available. A few quadrats (see 4.6.3) per compartment may suffice where the vegetation is rather similar. A more accurate survey would result from a greater number of quadrats. This information can then be used to prepare a vegetation map. In Britain, NVC maps (see 2.1) are commonly prepared. These are not always appropriate for damaged bogs since the NVC describe "natural" vegetation communities which may not necessarily be represented. Accordingly, it may be more useful to devise a site specific scheme to describe the main variation within the site. An example is shown in Figure 3.1. The Yorkshire Peat Partnership covers such large areas of blanket peat and has to complete its surveys in a short period so it uses a transect and quadrat sampling approach to its vegetation surveys (see Appendix A2.5).

3.1.3. HYDROLOGY Bog management is nearly always tied to manipulating a site's hydrological regime. Accordingly, hydrological information is required. This has various uses:  The existing hydrology needs to be assessed before it can be altered. An imperfect understanding of the hydrology of a site can lead to poor hydrological control and, thus, wasteful use of scarce resources.  Before management measures are implemented, the manager ought to know the possible implications of management around the site. For example, drain-blocking may cause the majority of a site's discharge to exit via a different channel. That channel may not be able to cope with extra flow thus flooding a neighbouring land user (an unpopular move!).  Alteration of the hydrology of one part of the site may have significant effects in other parts of the site. Drain blocking of one area to raise water Figure 3.1 vegetation levels to the surface may cause unexpected backing up and flooding. More compartment map of Tailend commonly, water simply finds another exit via a different part of the site Moss, Scotland. causing the failure of a management scheme. The simplest way to assess the hydrological regime of a site is to draw up a hydrological map (see Figure 3.2). This map could detail the following features:

39


Conserving Bogs

3.1

Planning Conservation Management

 route and direction of flows (streams, erosion channels, flushes, seepage lines) - topographical survey may be required;  all anthropogenic drainage features: ditches, pipes, mine-shafts, channels, cracks, tile-drains etc.;  the main water catchments within a site (see Figure 3.2);  all inflows and outflows;  water shedding and water collecting areas;  diffuse flows and; 

any areas of permanent standing water on the site.

A useful approach is to combine aerial photography and ground mapping. API can be used to map all the obvious hydrological features. For lowland raised bogs ground survey is then required to assess the direction of flow. This can be ascertained by accurate levelling (see 4.2) or, more simply, by going out on a rainy day and seeing which way the water flows. For upland Figure 3.2 Hydrological map of Lenzie blanket bog with their more substantial slopes it is usually possible Moss, Scotland. to ascertain direction of flow from digital contour maps for all but the flattest areas. Once the main routes and directions of flow have been mapped, main catchments can also be mapped. Another type of useful baseline hydrological survey has been carried out successfully on Fenns and Whixhall Mosses. There, summer and winter areas of open water were mapped. When carrying out these types of mapping it is worth bearing in mind the following points:  On an undamaged bog, most of the flow is through the surface semi-aerated "acrotelm" layer (see 2.5.2). Flow is diffuse and direction of flows on often fairly level surfaces are difficult to detect. Piezometer networks (see 4.3.4.3) may be the only way to gauge flow direction.  On reasonably "natural" raised bogs, flow is generally from the centre to the edge of the bog exiting into a surrounding lagg stream or fen. However, since most raised bogs are far from "natural", flow patterns are usually highly altered. On Flanders Moss (Stirlingshire, Scotland) for example, drains, cut into the edge of the bog, act as water-collecting foci for the area immediately surrounding the drain. Increased flow in these areas seems to have caused the formation of a poorly defined channel running back towards the centre of the Moss. Thus, the channel now has a large catchment area. These types of problems are not always obvious; ideally a detailed contour map should be drawn (see 4.2).  The hydrology of "natural" blanket bog is much more complex than raised bogs. Sub-surface piping, complex pool systems, variable topography, sink holes, springs etc. all serve to create hydrological complexity. At its simplest, water travels by diffuse flow within surface layers in the direction of the slope. Many areas of blanket bog within Britain have been moor-gripped to improve grazing (see 1.9, A1.3.2) creating an artificial hydrological regime.  Saturated peat is not impermeable but does exhibit a very low hydrological conductivity (see 2.5). Water will seep very slowly through peat barriers and this may be an important pathway in some sites. Different types of peat have different conductivities. White or less humified upper peats (see 4.5.5.1) are more permeable than black, highly humified peat.  Sub-surface piping is a common feature on blanket mire and has been found on raised bogs (for example, at Flanders Moss).  Water can often be found upwelling onto the mire surface. Peat bogs may even initially form as spring-fed peat mounds (for example, Red Lake Peatlands, N.America: Glaser et al., 1981). Water may also exit within the bog. On Moss Moran (Fife, Scotland), most of the water exits into old mine workings located in the centre of the bog.  Where most of the peat has been stripped away to leave only thin layers of peat overlying mineral ground, surfacewater may exit the bog through the sub-surface. This only happens where the mineral strata below the peat are permeable. On some parts of blanket mires being restored by the Yorkshire Peat Partnership some drainage channels and erosion gullies that have eroded to the underlying mineral layer appear dry as water escapes through the subsurface. On Thorne Moors, underlying sandy deposits were probably originally saturated. Land drainage and water abstraction have caused ground water-levels to drop considerably allowing water to seep through the thin layer of peat 40


Conserving Bogs

3.1

Planning Conservation Management

remaining (after peat extraction) and exit into the ground aquifer. Similar problems are experienced at Engbertsdyksvenen.

3.1.4. TOPOGRAPHY Hydrological control also requires a knowledge of the topography of a site. At its simplest, this could just involve sketching topography onto a site map. Often, more detailed topographical survey is required. As a minimum, for small raised bogs, it is worth levelling (see 4.2, 3.1.3) the main water routes in the site, e.g. drains, erosion channels etc. This will help in deciding where to locate dams for example (see 5.1.2.1). More detailed topographical survey may also be required in areas which are likely to receive intensive management. For example, the topography of a block (sod) cut area may need surveying for effective management. For large and complex raised bog sites, where a high level of hydrological manipulation is required, it may be worthwhile to survey the whole site to provide a base-line information set. This can be carried out in two ways. The site can be surveyed using levelling equipment (see 4.2) which often requires a grid system (the greater the number of grid points, the more accurate the survey is). Alternatively, aerial photogrammetric mapping (see 4.6.6.1) can be used to automatically produce contour maps. Note, these are expensive (e.g. ÂŁ5,000-7,000 on a 40-100ha site) and their precision relates to the type of vegetation cover. Detailed topographic maps can also be used to assess the groundwater mound of raised bogs (see 2.5.2). Careful modelling of the bog can be used to solve conservation problems. It is important to note that surveying topography is expensive and time consuming. Topographic survey should only be contemplated if the results are genuinely required.

3.1.5. SPECIAL INTEREST – FAUNA AND FLORA Bogs harbour unusual vegetation given their extreme conditions of low pH, low nutrients and water-logging (see 2.4). In addition, there are a number of particular species which are now rare and restricted to a few sites. For example, Rannoch Moor (Scotland) contains the only British locality for Scheuzeria palustris (Rannoch Rush). It is often useful to record exactly where these species grow on a site to ensure that future management operations do not drastically affect the population. Similarly, particularly rare fauna should also be mapped. Many bogs are important invertebrate sites (see 4.7.3). Sometimes, their preferred habitat has resulted from damage. Management objectives to conserve a bog and invertebrate communities can conflict. Compromises and prioritising are then necessary (see 3.2). Mapping of rare species is both of interest to assessing the effects of management (which may encourage an expansion of these populations) and also acts as a management constraint map. Management operations can be tailored to take cognisance of the distribution of rare species.

3.1.6.SAFETY AND HAZARDS Bogs can be dangerous places. Whilst the oft-quoted tales of coach and horses being subsumed into the mire may be an exaggeration, there is a record of a man on horseback found, perfectly preserved, in a bog on the Slamannan Plateau, Scotland. Most bogs, however, are far too dry nowadays to present this sort of risk although artificial pools (such as dammed up drains) present a potential safety hazard. More commonly, on damaged bogs, the dried shrubby vegetation on dry peat presents a serious fire risk. Glasson Moss (Cumbria, England) burnt for 4 months in the dry summer of 1976 as a fire slowly burnt within the peat (Lindsay, 1977). The forbidding and hazardous nature of bogs has been both an advantage and disadvantage for their conservation. On the one hand, this aspect has kept people off sites so leaving some sites in a remarkably "natural" state. However, this view of bogs has also contributed to unchecked exploitation. Clearly, to alter this view, people should be encouraged to visit bog nature reserves. Given the inherent dangers associated with bogs, a base-line hazard/safety survey is essential. A convenient way to collate this information is onto a map. Safety/hazard information should include: 41


Conserving Bogs

3.2

Planning Conservation Management

 drain network indicating particularly deep and/or hazardous drains (e.g. drains which have vegetated over) and crossing points;  deep pits or fire-pools;  areas of unstable peat;  areas of severe fire risk;  hazards from derelict machinery or equipment;  game shooting areas;  wooded areas - danger from falling trees in high winds (trees on peat are always shallow rooted and are susceptible to wind-throw); and  emergency telephone locations. In addition, consult with the local fire-brigade to produce a fire-hazard map. This would detail access routes, areas of deep water, areas of high fire-risk, firebreaks, turning points for fire appliances and adjacent fire hydrants.

3.1.7. ARCHAEOLOGICAL, PALAEOECOLOGICAL AND HISTORICAL INTEREST Part of the interest in bogs relates to the richness of the archive found within the peat. The significance of these types of remains should be considered as equal to the nature conservation significance of the site. Usually, conservation of the two areas of interest requires the same types of management (Coles, 1995). Rarely, conflicts may arise. For example, in the peat fields, which enclose the remains of the Sweet Trackway at Shapwick Heath, the water-levels were allowed to drop to allow mowing of meadows famed for their floristic and invertebrate interest. This could have damaged the trackway. In response, nature conservation management was altered to accommodate both interests. Occasionally, there may be times where the two interests conflict. To identify potential conflicts and find appropriate solutions it is important to undertake a base-line survey of existing archaeological / palaeoenvironmental / historical interest. Again, mapping of these interests is useful. The Yorkshire Peat Partnership (YPP) employs specialist consultants to carry out this type of survey on all of its blanket bog restoration sites prior to any works taking place. The survey is a walkover survey to identify and map:   

Any historic environment or archaeological features not previously recorded on the Historic Environment Record. Any remains that are vulnerable to damage from peat restoration operations. Inspection of a sample of grips or eroding gullies for features, lithics or small finds.

The survey provides a traffic light system result: Red – important areas for archaeology where no works can take place without prior approval. Amber – important areas for acrchaeology where works can take place with care. Green – areas unimportant from an archaeological perspective.

3.2. EVALUATION AND SETTING OBJECTIVES Evaluating the features of interest of a bog and setting management objectives need not be a difficult process. The approach taken in this guide is to evaluate the damage a bog has suffered, set objectives and define actions (prescriptions) which ameliorate the effects of the damage (see 3.3). This approach entails 42


Conserving Bogs

3.2

Planning Conservation Management

the assumption that the desired objective of bog management is to switch bogs back to as "natural" a state as possible. For European raised bogs and much blanket mire, "natural" systems are ombrotrophic and Sphagnum dominated. Whether this type of ecosystem can be recreated from a damaged bog depends upon a number of different factors: Starting Conditions The degree of damage a bog has sustained affects what can be achieved. Objectives set should be realistic. For example, peat extraction may expose underlying clays. Acidic, ombrotrophic vegetation will not recolonise these surfaces. Instead, wetland restoration may lead to the development of fen communities which in turn, may, after hundreds or thousands of years, lead to the development of raised bog. An assessment of the starting condition through the base-line survey (see 3.1) is, therefore, useful. If, after assessing damage the bog has sustained and the resultant habitat, it is realised that a "natural" bog system cannot be recreated, rehabilitated, or maintained, then more realistic objectives should be set.

Legislative Responsibilities Various legal and land-use constraints should be checked whilst setting objectives. Of note are planning, wildlife, archaeological, hydrological and health & safety regulations. The following should be considered: 1. On (former) peat extraction sites, land may be subject to planning controls specifying working practice and after-use. Checks should be made with the relevant local authorities. Also, check for other possible constraints such as shooting rights, grazing rights, turbary rights, riparian rights, rights of way, common land and public utilities (pipelines and pylons in particular). 2. Wildlife legislation may also affect what objectives are set. In particular, due regard must be given to: (in Britain) species specially protected under the Wildlife & Countryside Act and associated amendments, (in the EU) the Habitats & Species Directive and the Birds Directive. 3. Additionally, British archaeological sites may have been designated under the Ancient Monuments and Archaeological Areas Act (1979). Similar legislation applies in other European countries. 4. The protection of archaeological and palaeoenvironmental sites is, at present, rather weak (in Britain, at least). This is because legislation applies to structures rather than more abstract concepts such as peat stratigraphy or potential or even likely archaeology. Given such inadequacies, site managers should seek to fill the ‘gap’. It is useful to consider the following when planning site management: 5.

 Undertake a base-line archaeological and palaeoenvironmental survey; this can be a field or desk-top survey.  Ask or fund archaeologists to undertake watching briefs if peat extraction occurs.  Liase with archaeologists in the management planning process.  Check on the palaeoenvironmental significance of the site with experts from local universities (usually located within geography or biology departments).  6. For large-scale hydrological management, licences need obtaining for water impoundment (greater than 25,000 m3 in the U.K.), abstraction, discharging water (in some circumstances) and works affecting watercourses. 7. Health & safety regulations (for example, the UK’s Health and Safety Act, 1974) and subsequent regulations also impact on setting realistic objectives. Finance An obvious constraint for bog conservation management is finance. However, setting desired objectives despite a lack of funding is important given that a good management plan can be used as a tool to seek funding. As a step towards achieving those ideal objectives, a set of realistic or operational objectives can be formulated. Costing projects is important in setting operational objectives. Aspects which would need 43


Conserving Bogs

3.3

Planning Conservation Management

assessing include: staff costs, capital costs (machinery, equipment, materials), contracting costs (for specialist advice or plant operation for example), monitoring costs and ongoing maintenance costs of works. Land Use Current or future landuse of a site should also be considered. Certain land-uses can coexist with bog management for conservation purposes. Light grazing, for example, may have benefits (see 5.4). Due consideration should also be given to changing land-use as a result of conservation management. Encouraging public access onto nature reserves, for example, is a desirable goal providing this does not affect the nature conservation interest of the site. Bogs are, though, sensitive to trampling so provision may need to be made for anticipated changes in visitor pressure (see 5.6) Consultation Given all these considerations, setting objectives is never as straight-forward as one may imagine. Different people, groups or organisations have different views on what should be achieved. Differing wildlife, land-use and recreational interests may conflict. An effective solution is to form a working party so that all interested peoples can give their views. The aim is to accommodate all or most of these views when setting out management objectives. This may not be possible; in which case, objectives must be prioritised to solve conflicts.

3.3. ACTION PLAN (PRESCRIPTIONS) DAMAGING IMPACTS AND SOLUTIONS 3.3.1. INTRODUCTION The next step in the production of a management plan is to devise a set of actions (prescriptions) which should achieve set objectives. In effect, an action plan is devised. For a given site, the types of actions necessary vary widely and this book can only guide rather than dictate land managers towards appropriate actions to manage bogs. The approach taken has been to assume that bog managers are attempting to switch a bog back to a more ‘natural’ state. In some cases, this may be impossible given the starting conditions and objectives and associated actions should be tailored accordingly (see 3.2). However, for many bogs, the types and impacts of damage are common and, with management, a more ‘natural’ state can be achieved. This section relates to the damage a bog sustains (see 1.8-1.14 and Appendix 1) and to the types of actions (and associated techniques) which could be pursued to ameliorate the effects of such damage. The following look-up tables are designed to couple commonly encountered forms of damage with various options and associated remedial techniques.

44


Conserving Bogs

3.3

Planning Conservation Management

3.3.2. PEAT EXTRACTION Extraction Method Traditional

Cross-link to Damage 1.8.2 A1.2.3

Management Options

Cross-link to Management -

Maintain or reinstate traditional methods.

Sausage / Extrusion

1.8.3 A1.2.4

-

1.8.4 A1.2.5

-

Milling

1.8.5

5.1

45

A system of raised baulks, flat fields and trenches is left when cutting stops. The drier raised baulks are frequently dominated by heath communities, whilst the trenches and fields, if wet, may still support an assemblage of bog species. 5.3

-

Maintain cutting.

Sub-surface drains can be difficult to re-locate and block effectively. If these are not blocked the site may continue to dry out. This practice has now been superseded by milling and sausage cutting for commercial operations.

-

Do nothing once cutting has stopped.

Rehabilitate old cuttings.

The potential for natural rehabilitation is limited by subsurface drainage, compaction from machines and shading from drying peats. During commercial operations the surface maybe stripped to facilitate mechanised collection of the peats.

5.1

Maintain cutting.

If ombrotrophic peat still remains and there is a local population of bog species all that may be required is to block existing drainage channels. The impacts from this method of extraction relate partially to the scale of operation. It can range from small-scale domestic extraction to large commercial workings.

-

Do nothing once cutting has stopped.

Baulk and hollow (sod)

Many abandoned peat fields show good signs of natural recolonisation. However, if drainage systems still operate, the site may continue to dry out.

5.1

Maintain cutting.

Rehabilitate old cuttings.

Where possible, cutting should be avoided in sensitive areas or those of particular conservation importance.

-

Stop cutting and do nothing. Rehabilitate cutting areas.

Vegetation is often thrown back into the cutting (shoeing) which promotes recolonisation. The relatively slow extraction rate also helps this process.

-

Relocate cutting.

Comments

Recolonisation of bog species can be encouraged by raising and stabilising waterlevels. The water storage capacity of a functioning acrotelm is high in contrast to peat. Rehabilitation success rests on developing a high water storage capacity on cutover peat - either by creating open water or encouraging Sphagnum growth. Difficulties may arise on larger sites when the surface of the cutting fields are at different levels. To maintain a regular waterlevel, a system of dams and sluices may need to be installed. The remaining raised baulks can be beneficial as retaining walls for impounded water and provide access routes. These may have to be reenforced with other materials. If the site has been abandoned for a number of years, tree removal may be necessary. There is very little potential to maintain nature conservation interest during the extraction process. Before extraction (which can last decades) begins, the surface is stripped and drains are installed. The water content of the peat is reduced by 80-90% prior to harvesting.


Conserving Bogs

3.3

Planning Conservation Management Maintain cutting adjacent to intact areas.

5.1.3 5.1.4

Rehabilitate milled fields.

5.1-5.3

The extraction zone may draw down the water table in the adjacent peat body. Considerable engineering works such as stepped edges and the construction of bunds may be required to help maintain waterlevels. The rehabilitation of milled fields can be a considerable financial undertaking. Where possible, rehabilitation works should be planned during the extraction programme, so as to optimise after-use conditions, site expertise and machinery. There may be very little ombrogenous peat remaining. If fen peat or mineral soils are exposed there is very little opportunity to recreate ombrogenous conditions. The remaining peat may be dried and oxidised lacking the physical properties required to develop a functioning acrotelm. Waterlevels within milled fields are characteristically low and subject to large fluctuations. The water storage capacity of a functioning acrotelm is high in contrast to peat. Rehabilitation success rests on developing a high water storage capacity on cutover peat - either by creating open water or encouraging Sphagnum growth. The maintenance of a stable, high watertable may be achieved through the construction of flooded lagoons. Unless local refugia for bog species exists, vegetation may have to be introduced from a donor site. Unless rewetting occurs soon after milling ceases the site may be colonised by undesirable species, notably birch and bracken. Wheeler and Shaw (1995) provide considerable detail.

For all peat cutting activities, ideally, an experienced archaeologist should monitor the work in case an archaeological find or other palaeoenvironmental information is unearthed.

46


Conserving Bogs

3.3

Planning Conservation Management

3.3.3. AGRICULTURE Activity Sheep Grazing

Cross-link to Damage 1.9 A1.3.3

Management Options Heavy grazing over winter period.

Cross-link to Management 5.4

Heavy grazing over summer period.

5.4

Light grazing over summer period. Grazing with cattle.

5.4

Cattle Grazing

1.9 A1.3.3

Wild grazing

1.9 A1.3.3

Unrestricted grazing from wild populations of deer and rabbits.

5.4

Burning

1.9 1.12 A1.3.5

Unrestricted burning.

5.5

1.9 A1.3.2 (1.10)

Do nothing.

-

Moor gripping

5.4

Block with peat dams.

5.1.2.6

Block with sheet dams.

5.1.2.2 to 5.1.2.5

Block with stone dams

Note

Comments This type of approach is not recommended where bog forms the dominant grazing range of the animal. Water tables are higher during the winter months and the wet ground is more prone to trampling damage. Also there is very little shelter from bad weather. The following effects are characteristic of this kind of regime: a decline in ling heather and subsequent dominance of hare’s tail cotton grass alongside a decline in bryophyte cover from trampling and increased areas of bare peat. The creation of bare surfaces may lead to larger scale erosion problems, particularly on upland slopes. Bogs offer a low nutrient diet so supplementary feeding may be necessary; this can lead to localised enrichment and nutrient cycling through dung dispersal. Sheep selectively browse purple moor grass (and other grasses), deer-grass and hare’s tail cotton grass in early spring. Scrub species such as birch may also be selected when in leaf. However, the benefits of scrub control must be weighed against the potential damage caused by trampling. Damage from trampling is minimised as stocking levels are reduced. The use of cattle is not recommended on wet bog because of excessive poaching. However, given a selective preference for grasses, shrubs and scrub (in leaf) by cattle, they may be beneficial for degraded sites (prior to rewetting) where the surface is less prone to poaching. Red deer may compete with sheep for grazing in winter and early spring. Supplementary winter feeding concentrates damage through trampling and nutrient enrichment. However, where natural populations of wild grazers have access to bogs (blanket and raised) there may be some benefit given selective browsing of scrub. Burning on wet bog areas (or those dominated by Sphagnum communities) should be avoided as severe burns destroy vegetation and expose bare peat surfaces. Burning on peatlands should only be conducted in accordance with the Muirburn code. Large areas of blanket bog have been drained by moor-gripping. These closely spaced shallow drains quickly dry-out the acrotelm to leave a vegetation dominated by dwarf shrubs. Even when they have naturally infilled they continue to function as drains. Small peat dams can be installed either by hand or by machine; machines are usually quicker and cheaper. Ideally, dark peat should be used and the vehicle fitted with tracks to achieve very low ground pressure. Where the drains still have a reasonable depth of peat at the base they drain can be effectively blocked with a dam made from timber, plywood, plastic coated corrugated iron or plastic sheet. Where the drains have eroded through to the base substrate peat dams are often bypassed by water flowing underneath the dam and constructed dams are also difficult to seal to the base of the grip leading to further erosion. In these circumstances stone dams that trap eroding peat sediment are more effective.

The term heavy grazing relates in this instance to >1 sheep/ha. This figure is, however, relative to the starting conditions of the site. For instance, wet, Sphagnum dominated bog would be damaged by a stocking density of less than half this value. 47


Conserving Bogs

3.3

Planning Conservation Management

3.3.4. DRAINAGE Drain Size DepthxWidth Small drains 0.5m x 0.5m

Cross-link to Damage 1.8 1.9 A3.2 A3.3.2 (1.10)

Management Options Do nothing.

Block drains with peat dams.

Block drains with small sheet dams.

Medium sized drains 1m x 1.5m

1.8, 1.9 (1.10) A3.2 (A3.3.2)

Do nothing.

-

Shallow drains dry out the acrotelm with a subsequent loss of peat forming vegetation. Typically this effect is localised and is shown by a band of shrub and scrub species colonising along the ditch line.

5.1.2.6

Small peat dams can be installed either by hand or by machine; machines are usually quicker and cheaper. Ideally, dark peat should be used and the vehicle tracked or fitted with low ground pressure balloon tyres.

-

A drain can be effectively blocked with a dam made from plywood, plastic coated corrugated iron or plastic sheet. Although these dams may be more effective than peat they are more expensive. Correct positioning requires levelling. On sloping ground, these ditches can cause considerable erosion and ditch scour problems. Medium sized drains cut into catotelmic peat considerably altering bog hydrology..

5.1.6

Peat dams of this size require an excavator for construction; the peat used should be of a high enough humification (see 4.5.5).

5.1.2.4 4.2

Drains this size can be blocked with plastic sheet. Although these dams may be more effective than peat they are more expensive. Correct positioning requires levelling.

Block with solid wooden planks.

5.1.2.2

Plank or board dams have been used successfully to block ditches of this size and larger. Though time consuming to install they provide a long-term solution.

Block with plastic piling.

5.1.2.8

Plastic piling, though initially more expensive than some hardwoods, is durable. One of its advantages is that it can be quickly and easily installed either by machine or hand.

Block with a composite dam.

5.1.2.7

A composite dam is constructed from a combination of peat and an impermeable membrane or sheet. The peat merely acts as a support to the impermeable sheet. Compacted peat sandwiched between two boards can act as a bridge for occasional pedestrian or stock access.

Block with plastic sheets.

1.8, 1.9 1.11 A3.2 A3.4 A3.5

Comments

5.1.2.3 5.1.2.5 4.2

Block with peat dams.

Large drains >1.5m x >2m

Cross-link to Management

Do nothing.

-

Large drains are very damaging especially where the drain cuts into the mineral soils beneath the peat. Guidance from an engineer should be sought before attempting to block very large ditches.

Block with plastic piling dam.

5.1.2.8

Plastic piling can be used to breach quite large ditches. It can be strengthened with vertical or horizontal battens if required. Large dams are best installed by machine. Plastic piling is particularly effective when used to block very wide, but shallow ditches.

Block with composite dams.

5.1.2.7

A composite dam made from plastic piling and peat (to add support) is a quick and relatively cheap method of blocking large ditches.

48


Conserving Bogs

3.3

Planning Conservation Management

3.3.5. AFFORESTATION Trees Self-sown trees

Cross-link to Damage 1.14 A3.7.2

Management Options Do nothing.

Cross-link to Management -

Kill trees in-situ.

5.3.4 5.3.4.2 5.3.4.4

Cut with no herbicide application.

5.3

Cut and apply herbicide. Immature or open-canopy commercial plantation.

5.2.3

Do nothing.

Fell and remove trees.

-

(5.1) 5.3.1 5.3.2

Fell and leave.

Closed canopy mature plantation

(5.1)

5.3.1

Harvest by standard methods.

-

Harvest by alternative methods.

5.3.1 5.3.2

49

Comments Scrub and tree encroachment causes a decline in typical bog species. In-situ killing of trees can be achieved through herbicide application to standing trees through notching or injection. Non herbicide methods include ring barking and flooding. Tree cover should be tackled at its root cause. This usually means that a programme of hydrological management as well as tree clearance is necessary. Trees capable of coppicing require secondary treatment. Nonherbicide methods include flooding, pulling, cyclical cutting and grazing. Herbicide can either be applied directly to the foliage by spraying or weedwiping or onto cut stumps. Initial damage is caused by drainage. As the trees develop, secondary drainage and the application of fertilisers further damages the bog. However when the trees are immature (i.e. not at closed canopy) some bog species are usually present. Ineffective drainage may cause the plantation to fail. Trees can be felled with chainsaws and removed by either low ground pressure forwarders or netted and lifted off with helicopters. Hydrological management should follow tree removal. Given suitable conditions, Sphagnum can grow over fallen timber. Blocking drainage ditches is difficult. Standard harvesting on deep peat is not amenable to conservation objectives. Disruption to the surface through vehicle pressure and brash may hamper re-establishment of a functioning acrotelm. Harvesting trees with a view to rehabilitation is at the present experimental. There has been some experimentation with whole tree harvesting by helicopter and low ground pressure forwarders. Both these methods aim to reduce disturbance to the surface and maintain optimum conditions for re-establishment of bog species.


Conserving Bogs

3.3

Planning Conservation Management

3.3.6. OTHER TYPES OF DAMAGE Description Occasional Pedestrian Access

Cross-link to Damage 1.12 A1.6.5

Management Options Do nothing.

Cross-link to Management -

Provide Access Facilities.

Frequent Pedestrian Access

Use of Vehicles

Peat Erosion

1.12 A1.6.5

1.12 (1.10) A1.6.6 A1.5.2

1.14

5.6

Do nothing.

-

Re-route access.

-

Provide temporary access facilities.

5.6.4 5.6.6

Provide permanent access facilities.

5.6

Do nothing.

-

Re-route access.

-

Provide temporary facilities.

5.6.8

Provide Permanent Facilities

5.6.7

Reduce recreational pressure. Change grazing regimes. Change burning regime. Re-vegetate bare peat.

5.6

Experimental methods.

The site should be regularly assessed for signs of damage. If trampling damage becomes evident, access provision should be considered. Access provision is required if a bog has a low carrying capacity - itself determined by vegetation and peat characteristics. Wet, Sphagnum-rich bogs are more sensitive than degraded, heather dominated sites. Permanent provision can take the form of raised or floating boardwalks and footpaths, whilst brashings, pallets and mesh can be used for temporary provision Even bogs with a high carrying capacity can become damaged from heavy pedestrian use. Peat is rapidly eroded once vegetation is trampled and the surface exposed,. Where pedestrians are encouraged or expected some kind of permanent provision should be offered or the access re-routed. For management or non-interpretative access, sensitive or wet areas should be avoided. Access points come under considerable pressure during management operations. Damage can be limited by laying down netting, wooden pallets, duckboards or plastic paths. Footpaths and boardwalks make access easier for the pedestrian and help to contain pressure to one point. Even low ground pressure vehicles can damage the bog surface as the shearing motion of tyres and tracks damages fragile vegetation. Tracks widen as they re-route around previously damaged areas. Where possible vehicle routes should avoid wet or steeply sloping ground. Wooden boards and geogrids can be laid to provide temporary protection from vehicle damage. The construction of permanent roads and tracks should be a last resort as their impact is considerable. However, where access cannot be re-routed damage may be limited and confined by constructing a permanent track. Re-route walkers away from eroded areas or provide access facilities.

5.4

Reduce grazing and trampling pressure.

5.5

Reduce frequency and intensity of burning.

5.2

Whilst changing recreational, grazing and burning regimes prevents erosion, once erosion has occurred, the priority should be to revegetate eroded areas. A variety of methods have been used to stabilise mineral soils such as geotextile grids, adding soil stabilisers etc. Some of these could be adapted to peat soils.

-

50

Comments


Conserving Bogs

3.4

Planning Conservation Management

3.4. REPORTING, MONITORING AND EVALUATION 3.4.1. INTRODUCTION On completion of the plan, management work can begin and too often this is where the planning process stops. Management works are carried out and never evaluated; some vital parts to the plan are never completed; opportunities are missed; records get lost under the pile of paper in the corner; monitoring equipment is vandalised and never replaced and so on. For a host of reasons, management is often less effective than the plan envisaged. To avoid this, the planning process must be maintained through good reporting, survey, monitoring and evaluation.

3.4.2. REPORTING An essential part of site management is to monitor the quality and quantity of work done. A useful way of reporting is to use site reporting forms (see 4.1.2) and project recording forms. Projects, which make up each action to achieve desired management objectives, can be recorded by using standard forms. The NCC project recording form, for example, records: site, project, description, compartment, months active, priority, photographic record, recorder, labour, costs and notes. The information can be collated either on paper in a site management file or on computer. Database software is particularly appropriate for this type of information and the Countryside Management System has been specifically designed for this type of operation. Reporting and on-site monitoring should be carried out every time the site is visited. This may be just checking that all is OK or it may be more formalised by filling in site recording forms (see 4.1.2).

3.4.3. SURVEY AND MONTORING As the plan proceeds, extra survey and monitoring activities should take place (indeed, it is often integral to the plan). This has two main purposes: enhancing base-line survey information and monitoring the effectiveness of management. 3.4.3.1 Enhancing Base-line Survey Information In the initial plan, base-line survey information may be necessarily limited. The NCC’s suggested minimum management plan suggests that a brief description of the site followed by an evaluation of site features is enough in many instances although, as explained above, more detailed information is nearly always required for peatland management. However, extra base-line survey information may include: more information on specialised species such as invertebrates (see 4.7.3) and rare flora (see 4.6); more information on the hydrology of the site (see 4.3); greater information on the archaeology and history of the site (see 1.6, 3.1.7); or further important information relating to the likely success of management, such as peat properties (see 4.5.5) and chemistry (see 4.4) for example. 3.4.3.2 Monitoring the Effectiveness of Management Whilst monitoring need not be time-consuming nor expensive, its application can be useful:  It is important to monitor the effectiveness of management to enable an effective review of the plan (see 3.4.3).  Monitoring discerns when systems deviate from an expected norm allowing re-planning of management activities or even emergency actions.  Monitoring adds to the base-line survey information used for the site description. More effective site evaluations can be achieved as the quantity and quality of information increases.  Monitoring is a research tool and results can be applied more widely.

All sorts of monitoring can be applied to assess the effectiveness of management. Of prime importance is the division of a scheme which can assess whether the objectives for site management are being obtained. 51


Conserving Bogs

3.4

Planning Conservation Management

However, there is always a trade-off with the resources available for achieving this. The various monitoring activities suggested should be planned into an integrated monitoring scheme. It is useful to follow the following format when devising a monitoring scheme: 1. Re-state management objectives for site management. 2. Formulate a set of objectives which monitoring should achieve. 3. Set out a series of techniques and methods which could be used to achieve those monitoring objectives. 4. Set out the resource implications for these methods and techniques in terms of labour and cost. 5. Optional: Modify monitoring objectives or methods/techniques if resource implications are too high and return to step 3. 6. Set out method for data collection and devise necessary recording forms. 7. Set out the way data is to be stored (devise spreadsheets if appropriate). 8. Set out the way data is to be analysed.

For example: 1

Management objectives

Raise water-levels (though damming) to restore typical lowland raised bog communities to the mire.

2

Monitoring objectives

To assess the success of damming and to assess the rate of vegetation change.

3

Methods

Automatic water-level recording; automatic rain gauge; whole site monitoring using random quadrat vegetation monitoring each year.

4

Resource implications

Capital cost: £2000; labour: (for one skilled professional) data collection - 4 days per year, data storage and analysis - 4 days per year (TOO MUCH).

3

Modified methods Resource implications

Four WaLRaGs, rain gauge and one permanent quadrat near a drain.

Data collection and storage

On prepared Excel spreadsheets.

Data analysis

WaLRaG and rain data plotted on same graph showing minimum and maximum water levels and monthly rainfall. Assessing target of minimum water-level not to drop below 20cm. Quadrat data plotted as 3-D columns across the quadrat for each species and as summary percentages of all species. Assessing target of 90% ground cover by bog Sphagnum species.

4

5-7

8

Capital Cost: £200; labour (for volunteers) 12 ½ days per year - reading WaLRaGs and rain gauge; (for skilled professional) one ½ day for quadrat survey and one day for analysis of data, per year.

Generally, monitoring schemes are designed to gauge the impact and degree of success of management works and allow successful techniques to be highlighted for use elsewhere. Monitoring also has the sideeffect of allowing site managers to become more familiar with sites in a structured way. On bogs, the success of conservation management nearly always relates to the way hydrological factors and vegetation respond (they are, of course, inextricably linked). Often, it is vegetation change or stability which is sought although this may be underpinned by hydrological control. In these cases, it may only be necessary to monitor vegetation alone (see 4.6). Normally though, vegetation change is too slow to allow plans to be reviewed so some form of hydrological monitoring is carried out (see 4.3). As a consequence, the best approach is to integrate both vegetation and hydrological monitoring. Monitor hydrology to directly assess 52


Conserving Bogs

3.4

Planning Conservation Management

the effectiveness of hydrological control works (see 5.1) and integrate this with vegetation monitoring to assess the effect that has on the site. When planning monitoring schemes, bear the following points in mind:  Always clearly state the reason for monitoring before embarking on any particular scheme. Whilst this may seem obvious, it is too easy to collect data without clearly understanding its use. As a rule, if you are not sure why the data is being collected then seek advice or stop collecting it!  When monitoring the effectiveness of management, it is necessary to monitor before and after management works in order to provide a comparison. Monitoring after management only assesses the new situation which may not have changed. This is not always possible in which case, a desired target should be set (e.g. an average water-level of 10cm or less below the surface) and monitoring performed to see whether the target is achieved.  Bear in mind what data exists before the new phase of monitoring. Ensure that any new data collected can be meaningfully compared with previous data.  Consider whether the techniques are appropriate or sensitive enough to detect likely changes. Measuring vegetation change using a three point scale, though easy, may not pick up subtle changes (see 4.6.3).  Consider the appropriate recording time-interval - a compromise between time resources and what is required is necessary. Fixed point photographic monitoring of vegetation (see 4.1.3) on fairly stable sites may only need to be done every 5 years. Dipwell monitoring (see 4.3.3.2) may require weekly readings to be meaningful.  Consider the quality and quantity of data. It is too easy to collect lots of information which is of little use due to poor monitoring planning or because the data may be difficult to analyse.  Consider how the data should be stored. It is useful to set up spreadsheets on a P.C. which enable the data to be easily analysed. Blank forms, mirroring the spreadsheet, can then be printed out (on waterproof paper if necessary) to be used in the field. This helps to minimise recording mistakes.  Consider how the data is likely to be analysed - this helps in setting up recording forms and spreadsheets.  If water-levels are monitored to assess the effect of management (a damming programme for example), always measure some climate variables (rainfall in particular) to check whether the rise in water-level is not simply the result of wet weather (see 4.3) rather than because of management works. Alternatively, arrange to receive the same data from a near-by meteorological station.

3.4.3. EVALUATION AND UPDATING Good reporting and well planned and executed monitoring schemes should leave the manager of a site in a much better position to update the plan. Management plans are normally written for a five year period although this can vary according to the complexity of the site. Plans for new, complex or poorly understood sites may have to be revised after two or three years as rapid changes take place or a greater understanding of the site is gauged from survey and monitoring programmes. For a reasonably undamaged bog, a plan may only need revision once every 10 or 20 years. Revisions are likely to stem from the following:  Greater survey information reveals factors which had not been taken into account previously. These might be the presence of rare species, a better understanding of hydrology etc.  New methods and techniques for management are devised which changes one’s approach to a particular management problem.  Monitoring reveals the success or failure of particular management schemes.  Constraints on management approaches change.

Note that the management plan should be a concise document which is easy to use. Any necessary supporting material should be added to appendices. These may include detailed habitat survey or technical annexes for example.

53


Conserving Bogs

Monitoring and Site Assessment

PART 4 MONITORING AND SITE ASSESSMENT In Part 3, much was made of the need to plan conservation in order for it to be effective in achieving the desired objectives within set costs. The process (see 3 - Deriving a Management Plan) follows four stages: (1) description, (2) evaluation and setting objectives, (3) action planning and (4) reporting (including monitoring and evaluation). In this section, a series of methods and techniques which are likely to be used in the implementation of stages 1 and 4 of the management planning process are outlined. The descriptive part of the process mainly concerns site assessment whilst stage 4 requires monitoring of management operations as well as the progress of the plan itself. It is particularly important to check whether the plan is being adhered to and whether any agreements (with other people or organisations) are abided by. In practise, the methods used for both stages 1 and 4 are often the same. For example, a site assessment of the general condition of a bog and its vegetation may be conducted using aerial photograph interpretation (API - see 4.6.6.1). This information could then be used as part of the site description. However, after conservation management has taken place, a re-survey may be used to assess the effectiveness of management. Exactly the same techniques could be employed; this time collecting information for stage 4. The methods and techniques for site assessment and monitoring of bogs vary considerably in their complexity and cost. Simple subjective and qualitative field assessment (see 4.1.2) can yield extremely valuable information such as the impending failure of a major dam for example. The usefulness and ease of such monitoring means that it is usually conducted as a matter of course by site managers. Other methods are more complex and costly often requiring the services of a specialist. For example, using lysimeters (see 4.3.5) is a complicated endeavour although is essential if a bog’s water-balance equation is to be calculated (see 2.5.2). Whatever methods and techniques are used at a particular site, note that monitoring may be costly in terms of time and money. It is, therefore, particularly important to plan monitoring schemes carefully (see 3.4.3). Having urged caution, conservation management suffers from poor evaluation and reporting (see Introduction). Further, monitoring and evaluation are an integral part of the management planning process and should always be incorporated into management schemes. Good evaluation allows the management planning cycle to be completed. In this part, the main methods and techniques used for monitoring and site assessment are outlined. Methods and techniques which are directly related to bogs are covered. Other methods/techniques, which are common to many habitats, may be used on bogs and, in general, the reader is advised to refer to more specialist texts although for some of these common methods. Part 4 is laid out in the following sections: 4.1 GENERAL SITE MONITORING 4.1.1 Introduction 4.1.2 Field Assessment 4.1.3 Fixed Point Photograph Monitoring 4.2 TOPOGRAPHY 4.3 HYDROLOGY AND RAINFALL 4.3.1 Introduction 54


Conserving Bogs

Monitoring and Site Assessment

4.3.2 Rainfall 4.3.3 Water Levels 4.3.4 Seepage/Discharge 4.3.5. Evapotranspiration - Lysimeters 4.4 CHEMISTRY 4.4.1 Introduction and Sampling 4.4.2 pH 4.4.3 Conductivity 4.4.4 Redox Potential 4.4.5 Laboratory Techniques 4.5 PEAT 4.5.1 Introduction 4.5.2 Peat Depth 4.5.3 Surface Level Changes 4.5.4 Sampling Peat 4.5.5 Peat Properties 4.5.6 Peat Erosion 4.6 VEGETATION 4.6.1 Introduction 4.6.2 Marking Monitoring Positions 4.6.3 Using Quadrats 4.6.4 Data Storage and Processing 4.6.5 Proxy Measurements 4.6.6 Remote Sensing and Image Interpretation 4.7 FAUNA 4.7.1 Introduction 4.7.2 Birds 4.7.3 Invertebrates

55


Conserving Bogs

4.1

Monitoring and Site Assessment

4.1 GENERAL SITE MONITORING 4.1.1 Introduction Most of Part 4 discusses the monitoring of specific variables. This section addresses less technical approaches for more general site monitoring. The main aim of these schemes is to record the following:  management operations;  site structures, such as dams, boardwalks and bunds;  associated habitats, such as woodlands, grasslands;  habitat boundaries; and  other types of information such as visitor numbers. Proper planning is required even though this type of monitoring does not involve complex scientific methods or sophisticated analysis techniques. The aims and objectives of a scheme should be defined and all resources identified (see 3.4.3). The type of information generated (mainly descriptive and pictorial) is not readily quantified although it does form an informed basis for evaluating management work and assessing whether management objectives are being reached. For a full description of the Yorkshire Peat Partnership monitoring protocol and field survey forms see Appendix 2. 4.1.2 Field Assessment Field assessment involves recording major site features through standardised recording of observations and planned and unplanned events. A standard recording form is useful. Possible applications include:  a visual assessment of waterlevels in ditches, for example, comparing summer and winter levels;  an inspection of management structures such as dams, bunds and boardwalks;  an inspection of natural site features such as pools and rare plant communities; and  a record of unplanned events and observations. The information is best kept as a paper record of site development, management and observations. An example of a standard recording form is in Figure 4.1. This is easily customised and can be stored as a paper copy or entered onto a computer database to allow fast access to and analysis of the information. Alternatively, a computer based recording system, such as the Countryside Management System, can be used (see 3.4.2) where the record is complex and sophisticated. 4.1.3 Fixed Point Photograph Monitoring Taking a series of photographs of the same view or object from the same point at different times provides a visual history of change. As with any monitoring scheme, it is important that it is well planned (see 3.4.3). This type of approach is a valuable way of monitoring sites that are visited infrequently or where resources are limited. 4.1.3.1 Planning When setting up a monitoring scheme using photographs consider the following:  Diversity of habitats: try to include each habitat that is important to the management of the site.  Resource implications: time taken to collect and collate data and all relevant costs.

56


Conserving Bogs

Monitoring and Site Assessment

Yorkshire Peat Partnership works monitoring form

4.1 Site Name: Recorder:

Date: Weather conditions:

Time:

A. Grip Blocking with Peat Dams Record following using GPS mappers for dams on or within 5m of transect dams: Dam intact No signs of erosion around dam Water retained to base of previous dam Excess water dispersed without erosion Grip surface revegetating Species re-vegetating grip surface

YES/NO YES/NO YES/NO YES/NO % cover % cover

B. Grip / Gully Blocking with Timber / Heather Bale Dams Record following using GPS mappers for dams on or within 5m of transect dams: Dam intact No signs of erosion around dam Water retained to base of previous dam Sediment retained to base of previous dam Water surface revegetating Sediment surface revegetating % of water surface revegetated (viewed from above) % of sediment surface revegetating (viewed from above) Species re-vegetating gully surface (Table 1)

YES/NO YES/NO YES/NO YES/NO YES/NO YES/NO % cover % cover % cover

C. Reprofiling Record following using GPS mappers in 2m x 2m quadrats for reprofiled areas on or within 5m of transect: Reprofiled area intact (assess whole patch) YES/NO Signs of erosion to reprofiled area (assess whole patch) YES/NO Reprofiled area revegetating (assess whole patch) YES/NO % of quadrat area revegetated (viewed from above) % cover Number of grass nurse plants per quadrat No. % cover of grass nurse in quadrat (viewed from above) % cover Species re-vegetating in quadrat area (Table 1) % cover

D. Bare Peat Treated Areas Record following using GPS mappers in 2m x 2m quadrats for bare peat on or within 5m of transect: Bare peat area revegetating (assess whole patch) YES/NO % of bare peat area revegetated (assess whole patch) % cover Number of grass nurse plants per quadrat No. % cover of grass nurse per quadrat % cover Species re-vegetating quadrat surface (Table 1) % cover

Fig 4.1 An example of a site recording form used to assess changes following restoration works. This very same information is recorded using a drop down list on a handheld GPS device. This makes recording variables faster and more accurate.

57


Conserving Bogs

Monitoring and Site Assessment

4.1

 Figure 4.2 A handheld GPS device can be used to download base maps and create drop down recording forms to ensure accurate monitoring.  Purpose: critically assess what can be gained from each shot (avoid similar views).  Flexibility: points may be added or deleted over time. Note that presently accessible positions may become less accessible as a result of management, for example, flooding operations.  Frequency: the time between taking photographs should be assessed in relation to likely changes on the site. For rapidly-changing sites, photographs should be taken often; where sites are stable, photographs need only to be taken once every 5 or even 10 years. Examples are given below: Landscape views showing limited 5+yrs detail of vegetation and structures. Scrub encroachment.

2-5yrs

Management features, such as dams 1-5yrs and bunds. Detailed vegetation features (close- 5yrs ups) on stable sites. Detailed vegetation features (close- 2yrs ups) on changing sites.  Integration: Photographic monitoring should be integrated with other site monitoring as part of an integrated plan (see 3.4.3).  Location: Select locations that can be used for more than one view; this not only saves time in the field but also reduces the number of markers required. Consider also the following:  Repetitive shots of large areas of 'homogenous' vegetation are not particularly useful when recording vegetation cover. Aerial photography (see 4.6.6.1) is better for showing shifting vegetation boundaries.  Any elevated vantage point, on or more usually off the bog, can prove useful.  Time of year: Take photographs at the same time of year as areas of open water change during the year and vegetation dies back during winter. Winter weather is unpredictable and can prevent monitoring (for example, snow, fog).  Displays/talks: Photographs are useful for displays, talks, publications, websites and social media. An example of a fixed point photograph monitoring scheme is shown in Figure 4.3.

58


Conserving Bogs

Monitoring and Site Assessment

4.1

Figure 4.3 An example of fixed-point photograph locations. Key to fixed point locations: 1. Woodland edge and encroaching scrub. 2. Centre of bog and fixed quadrat location. 3. Cutover bog area and east boundary. 4. Mature woodland. 5. Open bog and western boundary. 6. Open bog and drain lines with encroaching trees. 7. Dam, drain and western boundary. 8. Dam and drain, 9. Open bog. 10. Encroaching scrub. 11. Site overview. 12. Site overview. 4.1.3.2 Marking Fixed Points Photographic positions should be marked in the field and on a site map to allow positions to be relocated particularly important given that different people will probably be involved. It is recommended that each position is marked with a letter (e.g. A, B, C etc.) and each subsequent shot taken, from that position, given a number (e.g. A1, A2, A3 etc.). If more than one site is being recorded, a unique site identification letter(s) should be added (e.g. for Flanders Moss - FMA1, FMA2 etc.). As photographic monitoring is a long-term programme it is important to use field markers that are not easily lost or moved. Several options exist:  Reference to permanent structures on and off site (i.e. take bearings and distances - see 4.2). This option, though time consuming, is a useful back-up if field markers are lost or moved.  Wooden posts: (untreated softwood may need replacing every 4-8 years depending on species). Posts should be pushed at least 1m into the peat to prevent vandalism. Mark posts with painted, etched or stamped code.  Metal posts: old scaffolding poles are a good alternative to wood. They are very robust and difficult to vandalise. Mark poles with painted, etched or stamped code.  Bamboo canes: not suitable as a long-term marker. They are easily removed or lost and difficult to mark effectively.  Electronic markers: relocation devices planted beneath the surface can be re-located by sweeping a transceiver over the surface; deters vandalism although expensive. 59


Conserving Bogs

4.1

Monitoring and Site Assessment

GPS devices can be used to record a point to an accuracy of centimetres but these devices can be very expensive. More affordable devices can measure to sub metre accuracy and cheaper commercial devices have an accuracy of 3-5 metres. Using GPS solely to record fixed points is not ideal but in the absence of permanent markers a good handheld GPS device is a viable alternative.

Any posts protruding above the surface may attract curious visitors and perching birds. Take one or two photographs of the fixed point itself to help relocation. 4.1.3.3 Taking the Photograph It is preferable to take more than one photo per vegetation quadrat in order to record wider site conditions. The following methodology is proposed in order to record vegetation as accurately as possible. Three photos can be taken per monitoring point;  A wider landscape photograph should be taken as a qualitative indicator of conditions. 

A photograph to record the immediate conditions of the monitoring point/quadrat.

A photograph in plan view of the monitoring point/quadrat. A tripod can be used to mount the camera.

Other considerations when taking a photograph include:  Place a scale marker in every frame in order to determine scale.  Record the orientation of every photograph to aid future continuity.  Record camera type, zoom, resolution and settings. Photography of quadrats has been successfully used to accurately determine changes in vegetation cover. If coupled with image classification using GIS it has been proven that is it is sufficiently accurate to measure vegetation cover change (Bennett et al 2000). It must be remembered though that it is an accurate method when analysing vegetation with a simple vertical structure but less so when analysing multi-layered vegetation.

Figure 4.4. Photographing the Yorkshire Dales and far, near and plan photographs of a fixed point quadrat. 4.1.3.4. Keeping a record Each image should be recorded on a standard recording form and if possible the location of the image on a handheld GPS device. The form can either be incorporated into the site recording form (Figure 4.1) or onto a separate form. An example of which is given in figure 4.5. Save all digital photographs in jpg format and catalogue in an excel spreadsheet using standard naming convention and sequential numbering. 4.1.3.5 Photographic advice Good quality digital cameras are now affordable and are being increasingly used to quantify vegetation change at the quadrat scale. Most digital cameras come with a pixel resolution of 10-15 which is more than adequate to generate high quality photographs. Most mobile phones also come with high resolution cameras and can be used if absolutely necessary. The best weather conditions for photographing vegetation are bright with some cloud (not bright sunshine). Evening and winter shadows obscure too much detail. 60


Conserving Bogs

4.2

Site Name: Recorder: Survey date:

Monitoring and Site Assessment

Site Information Grid ref: Weather conditions:

Owner: Address: Risk assessment completed and signed? Photo point Photo no. Bearing A1 1 3200 A2 2 3200 A3 3 1100 A4 4 1100

Time 11:00 11:10 14:00 14:05

Details Edge of eroding gully. Extensive area of bare peat. Heather dominated, flat. Hummock and hollows, some Sphagnum.

Figure 4.5. An example of a basic photographic form. 4.1.3.6 Camera platforms Bogs are flat and sometimes rather monotonous; photography is sometimes required at a scale between that possible on the ground and the scale used in aerial photography (see 4.6.6.1). For this, alternative camera platforms can be used. These include: fixed tower, "cherry-picker" (commonly used for repairing street lights in the UK!), telescopic boom arm, model aircraft, balloons and kites. There is greater control of viewing geometry with the first three types. It is also worthwhile considering the use of aerial photography obtained from UAV (unmanned aerial vehicle) technology. UAV’s are becoming increasingly affordable and are widely deployed to generate high resolution imagery and elevation data. With all these platforms, remember to ensure an adequate framework of ground control points.

4.2 TOPOGRAPHY The morphology of a bog is a key determinant of hydrology and vegetation. In many cases, management decisions can only be made given a detailed knowledge of topography (see 3.1.4). The methods and techniques used for topographic survey are generally common for most habitats and standard survey texts should be consulted. Note that independent reference markers should be sought when levelling. Independent reference points enable survey data to be related to a fixed datum which can be used as a reference point for future or additional surveys. An independent reference point can be provided by a peat anchor (see 4.5.3). The most appropriate independent reference points, however, are those that are long-term or permanent features such as large boulders, bedrock exposures and bench marks (U.K. ordnance survey reference marks). Ground survey techniques are used to investigate topographic features and their distribution. The size, distance and type of feature influences the choice of technique or instrument. Full information about using the more specialised survey instruments is not given. Reference should be made to specialist texts and the instruments demonstrated by someone familiar with their use. There is a large range of ground survey equipment available. The instruments most frequently used are described below. 4.2.1 Levelling frame Levelling frames are suitable for surveying small features up to 1m across such as a Sphagnum hummock; with care, they can be used across distances of two to three times the length of the frame. They are easy and quick to use, can be used by one person and are capable of fine vertical and horizontal resolution. 61


Conserving Bogs

4.2

Monitoring and Site Assessment

The frame (Figure 4.6) consists of a horizontal bar supported by a fixed or adjustable leg at either end. A spirit level is either secured to the bar or placed on it when necessary. A rule or self adhesive scale should be secured to the bar or a distance scale inscribed. Vertical holes to take needles can also be drilled at intervals as and if required. Dimensions vary but a horizontal length of 1.0 to 1.5m is the most practical size. Wood and aluminium are suitable materials for the horizontal bar, although 4.25cm diameter plastic pipe (fall-pipe) is also suitable. Fall-pipe is light and does not warp. Legs can be made of any suitable rod-shaped material such as, wood dowel or aluminium rod.

Figure 4.6 A levelling frame. A levelling frame is used in the following way:  Place the frame over the feature to be surveyed and push legs into the peat until they are secure.  Ensure that the horizontal bar is level and the legs are vertical.  Insert needles through holes in the bar at measured intervals until the tip is in contact with the bog surface and measure the length of needle protruding below or above the bar.  or: use a weighted (plumb) line to obtain a true vertical and measure distance from the bar, or a line inscribed along its side, to the bog surface. Repeated measurements should be from fixed points which can be relocated.

4.2.2 Plane Table This is a simple and relatively inexpensive form of survey which uses visual and graphic techniques for one person to produce a map in the field. It is most appropriate for mapping topographic detail in small areas. Over larger areas the errors are too great. The equipment is simple: tripod and flat wooden board covered by drawing surface (paper or similar). The board is held on the tripod by screws which allow it to be rotated and clamped. The sighting ruler (alidade) allows rays (lines) to be drawn from the known point (where the plane table is situated) to unknown ones. There are several methods for using a plane table. The simplest is to set down a number of known points on the paper as a control framework. These are plotted accurately at the scale of the desired end map (for example, 1:500/1:1,000) and also marked in the field (for example, using ranging poles). The plane table is then set up over one of these control points and orientated by sighting to another, checked with a third. Once correctly orientated the alidade is used to sight onto unknown points and draw rays on the map. By transferring the plane table to another control point, reorientating it, then sighting onto all the unknown points again, a set of intersecting rays are produced (that is, points are located by triangulation). These procedures can be repeated from a third point to produce "triangles of error" on the unknown point locations.

62


Conserving Bogs

4.2

Monitoring and Site Assessment

Plane tabling can be enhanced to include height information using an Indian Clinometer. However, more commonly a microptic alidade is used. This uses the stadia principle and this needs a staff. So the basic simplicity of the method is lost! 4.2.3 Hand Levels (Abney level and Stadia) Hand levels are pocket-sized easy-to-use instruments. They can be used to measure both slope (Abney) and height (Abney and Stadia) changes and are suitable for investigating topographic detail over short distances of a few metres or for carrying out less detailed rapid surveys over greater distances. Over short distances, they can provide surprisingly accurate results if they are used with care and their limitations recognised. An Abney level comprises a short viewing scope to which a 180o scale is attached. The scale incorporates a movable indicator to which a spirit-level is attached. A windowed mirror in the scope enables the spirit level to be viewed alongside the target. A stadia level comprises a scope and a fixed spirit-level only. These levels are used in the following way: Setting zero: For those with access to the sea-shore or a large lake, zero on an Abney Level can be checked by setting the angle scale to zero and sighting the level on the horizon of the sea or lake with the horizontal wire in the scope lying along the horizon. The spirit-level bubble should then appear to bisect the wire. Adjust the bubble, if necessary, using the adjustment screws situated on the spirit-level. Method 1 (for short to long distance using an Abney Level)  Set the angle scale to zero.  Hold the level firmly against a pole or on a support of known height.  Sight on to a surveying staff with the spirit-level bubble bisected by the wire.  Read height on surveying staff.  Subtract height of level from height reading on staff to give height difference of bog surface between level and staff position (Figure 4.7).  The level can be sighted onto a staff or pole of the same height as the one on which the level is held. The angle at which the bubble is bisected by the wire is recorded. The surface height difference is calculated trigonometrically (Figure 4.7). Method 2 (rapid survey method for short to long distances using an Abney Level)  While standing on a level surface look through the scope holding it horizontally and note exactly where the cross-wire lies on the assistant. Assistant walks out a measured distance and the operator sights on to the same position on the assistant, bisects bubble with the wire and records the angle of slope.  Using the measured distance and angle of slope, the height difference is calculated trigonometrically.

A

63


Conserving Bogs

4.2

Monitoring and Site Assessment

B

Figure 4.7 Using an Abney level (method 1). The change in surface height between the level and the staff = y – x (A) and using an Abney level to calculate height trigonometrically. In this case; x=y (B). Method 3 (for measuring slopes over short distances using an Abney Level)  An Abney level can be used with a slope pentameter to measure angles of slope. The slope pentameter was developed for use on moderate to steep and intricate slopes. It is particularly suitable for measuring both transverse and longitudinal angles of erosion gullies. A slope pentameter can be made from well-seasoned wood or light-weight alloy and consists of a pivoting frame in the form of a parallelogram. The frame enables standard units of slope to be measured. Slope angles are recorded via a protractor scale (Figure 4.8). Figure 4.8 A simple slope pantometer can be constructed from wood or alloy. 4.2.4 Quick-set and similar levels Over long distances, these levels are time consuming to use but a closing error of just a few centimetres is achievable over a levelling circuit of one or two kilometres. They are suitable for surveying a wide range of features including microtopography, erosion gullies, surface shrinkage alongside drainage ditches and the overall macrotopography and morphology of bogs. In addition, some levels can be used to map the position and extent of features using tachometric techniques. This type of level is expensive but can usually be borrowed from educational and research institutions (or hired). Dumpy and similar levels require mounting on a tripod they have a larger and better quality scope than Abney levels but similarly rely on a built-in spirit-level to ensure that the scope is horizontal. A circular spiritlevel on the base of the instrument ensures that it is horizontal in all directions. Some instruments have a 360o scale within which the instrument can be rotated which can be used to fix the direction of a transect or a survey point. The scope contains a graticule with three horizontal lines. The centre line is the equivalent of the cross wire in an Abney level. Readings for the upper and lower lines are used to calculate the distance from the instrument to the staff. Using tacheometry and the 360o horizontal scale, the spatial distribution of features can be mapped.

64


Conserving Bogs

4.2

Monitoring and Site Assessment

These levels are used in the following way: Setting up the tripod and instrument  Place tripod on as firm a stand as possible.  When all readings are to be made from one or a few locations a platform can be constructed for the tripod using three planks and a few wooden pegs.  When the instrument is located on one of the points of a survey grid or line, use a plumb-line or built in sight to centre the tripod over the marker, and measure the instrument's height above the bog surface.  The instrument height must be measured accurately, as it links the foresight and backsight.  The level has to be levelled by using the footscrews to bring the bubble into the middle before taking the reading.  Make sure you have focused the graticule by focusing it on infinity.  Write readings down on standard booking forms (refer to surveying texts or instrument instruction manual). Setting out a line or grid  Survey lines - mark at measured intervals using garden canes or similar.  Survey grid - measure and mark out a baseline at one side or across the site. Set out grid lines at right angles to the baseline. To obtain a right angle use the 3, 4, 5 triangle system (Figure 4.9) or a right-angle sight (Figure 4.10).  The baseline should be permanently marked (see 4.1.3.2). Levelling a line or grid  Set up the tripod and instrument as described.  Place the staff on the survey points. Attach plastic, metal or wooden disks to the base of the tripod to help prevent it from sinking.  Sight the instrument onto the staff, focus and adjust the spirit-level (if the instrument is not self-levelling) and read the staff height scale (make sure the bubble is still centred - if it drifts, read as it crosses the centre and take an average of a few readings).  Over distances greater than 30m, it is advisable to move the instrument, "leap fogging" with the staff person, foresighting and backsighting onto the staff without moving the staff position before and after moving the level (Figure A.11).  Surveys that require repositioning of the instrument must be "closed". The first and last staff positions of the survey or section of the survey coincide. This acts as a check on the accuracy of the survey.  The difference between the start and end heights for each closed survey or survey section is known as the closing error. This error is apportioned equally between all survey points except the start point.

65


Conserving Bogs

Monitoring and Site Assessment

4.2

Figure 4.9 Align a grid line at right angles to the baseline by using the 3-4-5 triangle method.

Figure 4.10 Use a right angle sight to position a gridline at a right angle to the baseline.

4.2.5 Tacheometric surveying Tacheometric surveying techniques can be employed when time is short and the precision of a measured grid is not required. The stadia wires within the telescope are manufactured so that they represent a fixed angle. If the telescope is level, then the distance between them, as measured on the staff, can be directly converted to determine the distance the staff is from the instrument. With most instruments the ground distance is calculated by multiplying the interstadial distance by 100.

Figure 4.11 A “leap frog” survey used for surveying long distances requires foresighting and backsighting when the level is moved. Feature mapping  Instruments with a 360o horizontal scale can be used to provide a location map of features such as pools, ditches, monitoring sites and so on.  Hold the staff alongside a feature and point the scope at the staff. Read the angle of orientation on the horizontal scale and measure the distance between the instrument and staff tacheometrically.  Repeat at a number of points along or around a feature to determine the extent of the feature. 4.2.6 Theodolites The advantages of using theodolites are that they are accurate and versatile, measurements can be made over long distances and surveys require, therefore, fewer instrument stations. Disadvantages are their size, 66


Conserving Bogs

4.3

Monitoring and Site Assessment

weight and cost and that the operator needs adequate training in their use. If a survey using a theodolite is required it may be appropriate to bring in a skilled volunteer or contracted specialist. Theodolites have the same uses described for simpler instruments but come into their own when used for large or whole site surveys. There are two principle types of theodolite: those that are purely optical and those that incorporate an electronic measuring system. Refer to specialists texts for details on how to operate theodolites. 4.2.7 Electronic Equipment Many of the surveying techniques described above have now been superseded by newer electronic equipment. Of these the most useful are Electronic Distance Measurers (EDMs) and Geographic Positioning Systems (GPS). EDMs use reflective plates which reflect light back at the instrument to record exact distances. Measurements can be downloaded directly into computer software allowing much quicker survey. GPS relies on satellites. Instruments search and fix on a series of satellites orbiting above. GPS is becoming more and more accurate with positions now being fixed to within a few centimetres - good enough for the survey requirements of conservation management. Laser scanners are a relatively new technology which work by taking thousands of measurements very rapidly. The 3D points can then be manipulated to produce 3D drawings and surface models. 4.2.8 Aerial Photogrammetric Survey The other method of obtaining detailed contour maps is to use aerial photogrammetric survey. Light Detection and Ranging (LIDAR) is a remote sensing method that uses light in the form of a pulsed laser to measure distance from the ground. LIDAR instruments containing a scanner and a GPS receiver are commonly attached to aeroplanes and helicopters to generate precise 3D images of topography. Digital Elevation Model (DEM) is a digital model or a 3D representation of surface terrain. Specialist equipment consisting of a GPS system and digital camera is attached to an aircraft or UAV and a photograph is taken every few seconds. Specialist software is used to create 3D elevation models of surface terrain comparable to LIDAR.

4.3 HYDROLOGY AND RAINFALL 4.3.1 Introduction Bog management is invariably concerned with water (see 2.5, 3.1.3). Effective management, therefore, requires an understanding of the hydrology of a site and some form of hydrological monitoring to assess the effectiveness of management may be required. However, before embarking on hydrological monitoring, remember that results should always be compared to climate data. The main hydrological parameters (Table 4.1) measured are:  Rainfall (4.3.2): Measured using a rain-gauge or data collected from a local meteorological station.  Water-levels (4.3.3): Levels can be mapped using ground survey or using instruments which measure the actual level such as dip-wells, WaLRaGs, chart recorders, automatic level recorders, remote sensing and stage boards.  Discharge (4.3.4): This gives an idea of the seepage emanating from a site although it is only really useful on highly drained sites where water is lost at discrete points. V-notch weirs and tipping bucket flow gauges can also be used. The rate and direction of seepage may be measured by using piezometers.  Evapotranspiration (4.3.5): This is almost impossible to measure directly but can be measured using a lysimeter.

67


Conserving Bogs

4.3

Monitoring and Site Assessment

Table 4.1 A summary of the variables measured and how easy it is to collect the data. Variable Rainfall Water level

Pool water level Evapo-transpiration Ditch or streamflow Seepage

Method Collecting raingauge Recording raingauge Site wetness mapping Dipwells Walrags Water level logger Aerial infra-red Stage board Lysimeter Tipping bucket gauge V-notch weir Piezometers

Section 4.3.2 4.3.2 4.3.3.1

Easy? Yes No Yes

4.3.3.2 4.3.3.3 4.3.3.4 4.3.3.5 4.3.3.6 4.3.5 A6.3.3 4.3.4.2 A6.3.2 4.3.4.1 A6.3.2 4.3.4.3

Yes Yes No No Yes No No No No

4.3.2 Rainfall This can be measured directly using a rain-gauge or data can be sought from a local meteorological station. The simplest rain-gauges consist of a funnel set into a sharp-rimmed metal or plastic cylindrical container (Figure 4.12). Gauges cost between £30 -£180 or can be made for about £12. Snow-fall is more difficult to measure although car-battery powered heated bucket gauges can be used. More sophisticated designs tilting siphon gauges (£1600) and tipping bucket gauges (£2000) - can be used if the gauge cannot be regularly visited. Straight-forward gauges can be made from 40cm lengths of 10cm diameter PVC soil drainage pipe, with a joining collar. A disc, cut from 3mm PVC sheet, should be glued onto the bottom and a plastic funnel cut to size and sealed inside with bath sealant. A two litre plastic bottle should be adequate for monthly readings at lowland sites; though perhaps only for two weeks at an upland site (in Britain). The gauge should be sited in a typical part of the bog with its rim protruding 30cm above ground. Pack the gauge firmly into the Figure 4.12 A design for a simple collecting rain ground. Place duck-board near the gauge gauge to stop poaching and cut away any overhanging vegetation. The catch is measured using a measuring cylinder. Calibrated cylinders can be bought for standard rain-gauge in diameters of 127mm (5 inches) and 203mm (8 inches). Otherwise, use the following equation: R = c / 0.0785(rd)2 where R = rainfall (in mm), c = the catch (ml/cc) and rd = the rim diameter of the rain-gauge (in cm).

68


Conserving Bogs

The data can be displayed as a line charts along side water-level fluctuations. SMDW2

SMDW1 -4

-2

0

2

4

-6

6

0

0

10

10

Depth (cm)

Depth (cm)

-6

20 30 40

-4

-2

0

2

4

6

4

6

20 30 40 50

50

60

60 26/11/2009

21/05/2010

19/07/2010

26/11/2009

21/05/2010

19/07/2010

11/08/2010

15/09/2010

01/10/2010

11/08/2010

15/09/2010

01/10/2010

SMDW3 -6

-4

-2

0

SMDW4 2

4

6

-6

0 10 20

Depth (cm)

Depth (cm)

4.3

Monitoring and Site Assessment

30 40 50 60 70 19/05/2010

15/07/2010

15/09/2010

07/10/2010

19/08/2010

-4

-2

0

2

0 5 10 15 20 25 30 35 40 19/05/2010

15/07/2010

15/09/2010

07/10/2010

19/08/2010

Figure 4.13 Graphs showing dipwell data over time at 4 different areas.

4.3.3 Water Levels 4.3.3.1 Ground Wetness A map of site wetness is a surprisingly useful description allowing, for example, all- terrain vehicle (ATV) access to be devised and ditch damming programmes to be targeted. Assessing whole site wetness patterns can be achieved using the following technique:  Use a method to select a series of points for survey across the site, such as, a grid.  Put in a short post or stake to mark each observation point. Observation points should be accurately recorded so that the survey can be easily repeated.  Survey the bog once during summer and once in winter.  During a survey, judge the wetness at each observation point by recording:  surface water (yes/no),  a quaking surface on jumping (yes/no),  adjacent pools (within 20m) (yes/no),  Sphagnum dominated vegetation (yes/no),  and, at points which are not particularly wet, judge the dryness by observing:  sloping ground (i.e. slope more than 2o) (yes/no),  rabbit holes (i.e. within 20 m) (yes/no),  tree or heather dominated vegetation (yes/no),  adjacent ditches (i.e. within 20 m) (yes/no), This type of approach has not been extensively tested and although similar maps can be prepared by simply recording areas of open water in summer and winter. These are particularly useful for planning ditch blocking programmes and for assessing safety hazards on the bog. 69


Conserving Bogs

4.3

Monitoring and Site Assessment

4.3.3.2 Dipwells Introduction The commonest and easiest way to measure water-levels is to use dipwells. These are simply perforated plastic tubes pushed into a hole in the ground. Dipwell diameters range from 8 mm (microbore) to 5cm and can be constructed from perforated plastic pipe or solid-walled pipe with holes drilled in. A cap should be fitted over both ends: on the base to stop peat up welling into the dipwell (these are not always fitted and are not necessary for firm peats and microbore dipwells) and on the top to keep out snow, mice and insects. The dip-well can be fixed to the surface by adding a flanged collar (Figure 4.14); this is useful as dipwells should not be moved once recording starts. The duration and frequency of monitoring should be chosen to suit particular circumstances. Note the importance of monitoring before as well as after management operations so that any resulting changes in water level can be demonstrated by comparing the averages before and after. Since the water level is affected by the weather, take enough readings to get an average uninfluenced by weather. Six readings, at least a week apart, are sufficient provided that they are taken during the winter and not more than two are taken on days when the weekly rain-gauge catch is less than 5 mm. For example, if monitoring is undertaken to find out how successful a ditch damming programme is in raising the water table, readings may be taken at weekly intervals for 6-10 weeks before the damming and the same afterwards. For short-term monitoring of this type, it is best to avoid summer and early autumn because the water level is usually drawn down by warmer and drier weather. For longer-term monitoring, the frequency can be reduced to monthly intervals especially if the dipwell data is supplemented by WaLRaG data (see 4.3.3.3) to measure the range of water table fluctuation between monthly readings. Figure 4.14 A design for a dipwell with a flanged collar. The cap aids visibility as well as keeping out snow, mice and insects. Locate the dipwells in positions of average ground level (carpets, flats and so on), avoiding hummocks and hollows. For ease of location, it is useful to align dipwells into straight transects although this may not be the most informative arrangement. A grid system may provide more useful information. It is also important to consider what, exactly, is hoped to be discovered. For example, dipwells should be placed within the management area if the measurements are to assess the direct effects of management. Whole site effects can be gauged by siting dipwells away from the main management areas. For ground water modelling or when the absolute water level is required, dipwells should be anchored to the substrate and levelled to a fixed level (such as ordnance datum). If it is simply the case of ascertaining the relative distance from the peat surface to the water-level, dipwells need not be anchored. 70


Conserving Bogs

4.3

Monitoring and Site Assessment

Once constructed, dipwells are placed in the peat either by pushing in or, preferably, taking out a core of peat so that the peat is not disturbed too much. It is useful to place a post marked with a piece of fluorescent tape (deters birds and makes it easier to find) close to the dipwell. The depth to the water-table (DWT) is calculated by measuring from the top of the dipwell to the ground surface and subtracting that from the top of the dipwell to the water level. Steel measuring tape can be used though specially made dipsticks which buzz or light up when the end reaches the water are more practical. For microbore dipwells, a fine plastic tube connected to a stethoscope is used. By blowing down the tube, bubbles are heard when the end touches the water (see Figure 4.15). Fully automated dipwells equipped with pressure transducers and data loggers are now available. These can set to record the water table level at predetermined intervals. Dipwell data is usually simply graphed against time (Figure 4.13) whilst transect data is plotted against distance. Grid data is usually plotted as isolines on a map. Figure 4.15 A stethoscope measuring device used to measure water levels in microbore dipwells. 4.3.3.3 WaLRaGs The WaLRaG (Water Level Range Gauge) is a dipwell which gives the current depth to water- table (DWT) and also shows the highest and lowest DWT since the previous reading. Lower extremes are particularly useful to know because this is a limiting factor for many typical bog species. WaLRaGs have also been used for archaeological monitoring - a particularly useful application. Various designs of maximum and minimum recording wells have been used in the past with varying degrees of success. Most have been home-made, but many designs are now commercially available. If the recording interval for measuring water-tables using conventional dipwells is long, it is useful to supplement this data with information derived from WaLRaGs. WaLRaG installation is as follows:  The pipe is installed by pushing it into a hole made with a suitable sized auger. Alternatively, you can use a knife. Make sure the hole is deep enough for the float to fall in dry weather.  Push the pipe down the hole and, with one foam block in the channel, lower the float down inside it, fitting the roller bearing into the channel.  Push the other foam block down inside the channel before screwing on the top cap.  Move the foam blocks so that they both touch the roller bearing. A week or so later, check that the bottle is afloat and decide whether the hole needs to be deepened to prevent the pointer from going off the bottom of the scale.  Once you have made any necessary adjustments, ensure that the pipe cannot slip or get pushed further into the ground by attaching a flanged collar fixed at ground level with two screws or a (treated) timber batten fixed in place with an angle bracket. Again move the foam blocks to touch the bearing.  Start reading the following week or month.  Ensure the foam blocks move freely and, if necessary, trim the blocks slightly to reduce friction.

71


Conserving Bogs

Monitoring and Site Assessment

The pointer shows the current reading while the upper block shows the maximum reading and the lower one shows the minimum reading since they were last reset. It is important to remember to reset the instrument by pushing the foam blocks back to touch the pointer after taking readings. Store the readings on paper or on a computer spreadsheet. The following technique for taking readings effectively allows for movement of the WaLRaG in the peat. Other methods have been used e.g. Bragg et al. (1994) and Ninnes and Keay (1994).

4.3

 With the float in place, use a dipstick or a tape measure to measure the distance from the bottom of the window down to the water level (Figure 4.16 A).  Measure the distance from the bottom of the window to the ground surface (Figure 4.16 B). Subtract B from A to give the current depth to water table (DWT).  Measure from the middle of the pointer to the bottom of the top block (Figure 4.16 C). Subtract this figure from the DWT, to give minimum DWT (the highest water level in the recording period). Figure 4.16 A WaLRaG or Water Level Rain Gauge, used to record maximum and minimum water levels

 Measure from the middle of the pointer to the top of the bottom block (Figure 4.16 D). Add this figure to DWT to give the maximum DWT (i.e. the lowest water level in the recording period).

When you have calculated the true depths to water table, look for any maximum or minimum values which seem markedly different from the rest. Look at the previous set of readings and decide whether the person reading them that day had forgotten to move the blocks back to touch the bearing. If so, discard the unreliable readings. When using WaLRaGs, refer to Bragg et al (1994). 4.3.3.4 Capacitance probes Overland flow can impact on the retention of groundwater and can influence vegetation. Carefully positioned capacitance probes can be used to measure overland flow. 4.3.3.5 Chemical Tracing Techniques Through flow can influence water table dynamics and can be measured using chemical tracing techniques, for example, sodium chloride (NaCl) and conductivity loggers. The measurements are expensive to resource both financially and time wise. Consequently, they are not usually integrated into a standard, resource limited, hydrological monitoring protocol.

72


Conserving Bogs

4.3

Monitoring and Site Assessment

4.3.3.6 Automatic Data Loggers Automatic data loggers can be used to measure a whole variety of variables such as flow rates and water levels. For water-levels, two types have been commonly used. Clockwork chart recorders, such as R-16s, have been used. They provide continuous paper water-level charts. Machines are usually set to chart waterlevel variations for a one month period before the chart is replaced. Continuous records of water-level can be extremely useful especially when addressing the pattern of water-level movement - a key determinant of a 'healthy' site (see 2.5.2). However, the data produced by R-16s is difficult to handle. To explore the data thoroughly, the chart is either read-off manually and inputted into a computer or the line is digitised allowing easier data manipulation usually in spreadsheet software. More usually, a specially designed data logger is used (for example, the Chambers Logger). These allow water-levels to be recorded every few seconds to every few days for up to 2 years. The logger often only needs to be visited once every six months and the data can be down loaded straight into computer spreadsheets. The software provides a graphical display of water level and gives minimum and maximum water level values. The time saved by visiting the logger infrequently and not having to input any data normally outweighs the capital cost of the equipment. However, before embarking on the use of data loggers, consider the following:  the property to be measured;  precision of readings;  reading interval;  site visits to download readings;  getting equipment out onto the bog;  vandalism or theft;  keeping the logger dry;  site temperature range required;  requirement for a portable computer to download readings;  mains power supply to monitoring equipment;  battery power, life, changes and cost;  use of solar or wind power to charge batteries;  need for an unbroken run of data;  tolerable gaps in the dataset;  ease of maintenance and operation;  the necessary equipment: sensors, cables, data logger, batteries (with charging system if necessary), data storage and transfer medium (i.e. data cards, cartridges, EPROMs or suchlike and appropriate readers) or portable computer, PC with software for storing, analysing and displaying data;  the logger's data storage capacity and battery life dictate the schedule of downloading/battery changing/general maintenance visits; and  insurance of equipment. Increasingly, wireless telemetry systems are being used to monitor real time changes in hydrological variables. Many systems rely on radio waves to transmit data to a receiver, in more remote areas batteries can be recharged using a small solar panel. This enables data to be received remotely, reducing site visits and increasing data manipulation efficiency. 4.3.3.7 Remote Sensing Water levels can be mapped by using multispectral remote sensing. Aircraft can be flown with an Airborne Thematic mapper which has spectral bands covering the visible, near infrared (NIR), short wave (SWIR) and thermal infrared. Spectral indices developed from NIR and SWIR liquid water absorbance are used to provide high resolution quantitative hydrological information. When coupled with in situ field measurements, 73


Conserving Bogs

4.3

Monitoring and Site Assessment

hydrological data is generated that has practical applications for peatland practitioners (Harris and Bryant 2009).

4.3.3.8 Modelling DEM images generated from aerial photogrammetry and LIDAR can be used to map surface water flow which is of particular use to assess the efficacy of grip and gully blocking techniques. Hydrological software tools within widely available and affordable Geographical Information Systems (GIS) can be used to model the flow of water across the peat surface when combined with DEMs. Generating hydrological information using such software requires specialist skills. Many other types of hydrological modelling such as Flow Map (Laine, S.N., and Milledge D.G., 2011) have been developed to measure and quantify peatland hydrological variables. 4.3.3.9 Satellites Soil Moisture Active Passive mission, SMAP, a NASA satellite set to measure soil moisture content using radar (launch date; November 2014) will provide soil moisture information at a resolution of 9km. Most restoration projects require finer resolution data sets to be practically applicable. 4.3.3.10 Stage Boards Stage boards are used to measure water levels of standing water bodies. Measurements allow long-term trends to be distinguished from seasonal fluctuations. They can also be used as a crude indicator of stream or ditch flow if it is situated in a place with a stable cross-section and a slow current. The board simply consists of a board capable of withstanding constantly wet conditions with a scale painted on it with numbers large enough to be read from a few metres away (Figure 4.17). A home-made stage board can be made for about ÂŁ10. It is useful to use binoculars to read it if the nearest accessible place is some distance away. Figure 4.17 A stage-board. The board shows the water level in standing water features such as a pool. The duck boarding is used to prevent damage to the bog surface.

Use an oak or elm board or a length of plastic piling to make a stage board. Paint the board white or black and use the contrasting colour for the scale. Start with zero at the lower end and mark off every centimetre, using a longer mark every 5 cm and label each 10 cm mark. The board can be fixed onto a post hammered into the peat. If the peat is too soft to get the post in firmly, fix the board onto a timber rail with the 1.0m mark level with the lower edge of the rail. Nail the ends of the rail onto wooden posts hammered in almost to ground level on two sides of the water body so that the board is partially submerged in the water and it can be clearly seen from firm ground. The lower edge of the rail should lie along the ground surface. Try to keep the structure as discrete as possible. Use a duckboard to reduce trampling at the place from which you intend to read the stage board. Data is used graphed against time; it is useful to show rainfall on the same graph. By plotting the relationship between the stage reading and the discharge, a stage reading can also be used as a surrogate for discharge.

4.3.4 Seepage/Discharge 4.3.4.1 V-notch weir Purpose A V-notch weir is an instrument for measuring the amount of water flowing along a ditch or down a stream. In terms of the water balance of an area of bog, this represents the lateral seepage component, since water 74


Conserving Bogs

4.3

Monitoring and Site Assessment

moving sideways through a bog usually moves near the surface and is intercepted by a ditch. The rate of flow, known as the discharge, is measured indirectly using a V-notch weir and a water level recorder. Description and appraisal V-notch weirs are widely used in the water industry and in hydrological research. They are specialist hydrological instruments and their use can involve considerable financial outlay and commitment of staff time. The weir forms a dam in the stream or ditch and the V shaped notch in its top edge acts as a spill-way. The discharge of the ditch can be calculated from a standard formula and is related to the stage or head of water above the base of the notch. A water level recorder is used to monitor the stage. The method of recording the water level determines the cost. Home-made clockwork chart recorders have been used but these need a lot of maintenance to work reliably. Many different types of water level recorder are available commercially. Chart recorders do not require mains nor battery power and are reliable although extra work is involved in reading off the levels and times from the chart. A more advanced type uses a float, counterweight and pulley arrangement similar to that of a chart recorder but converts the rotation of the pulley to a varying electrical signal using a multi-turn potentiometer and records it on a data logger. Waterlevel recorders based on pressure sensors are available commercially. These monitor the pressure difference between an underwater sensor and the atmosphere to convert it to a water level, usually relative to the sensor position. Other types of water level recorder based on capacitance sensors are also available. Expect to get some unreliable records during cold weather. Ice can form in the weir pool and although water usually continues to flow over the notch, the relationship between discharge and stage changes as ice impedes the notch. The water-level recorder may also record incorrectly during freezing conditions. If it has a float, this may become frozen into the ice and does not float properly until it thaws. Some of the most advanced V-notch weir models use a vibrating wire force transducer; as water levels change the changing buoyancy on a cylinder acts directly on the vibrating transducer and water level sensor. These can be attached to a data acquisition system for remote reading.

Figure 4.18 A V notch weir with a dipwell and a turbidity flow meter installed in the North York Moors. 75


Conserving Bogs

4.3

Monitoring and Site Assessment

Method Some aspects of the design and calibration of V-notch weirs are very complicated. More information about design, calibration, hook gauge design and so on, can be found in British Standard 3680. A weir suitable for ditches and small streams on bogs can be made from any sheet material that can withstand constantly wet conditions and is resistant to corrosion by acid bog water. Marine plywood, plastic, aluminium or stainless steel are all appropriate. It should be strong enough to resist bending (thin sheets can be strengthened by fixing horizontal stiffening bars) and big enough to cut into the undisturbed sides and base of a stream or ditch by about 50 cm. The notch may be cut out of the top edge of the weir plate or alternatively, a separate notch plate can be bolted over a cutout in the weir plate and the gap sealed with silicone sealant. The latter arrangement allows the use of a relatively cheap material, such as plywood, for the weir plate with a more robust and expensive, stainless steel notch plate. The plate is inserted into a groove cut through the vegetation at both sides with a spade and is pushed or hammered down so that the notch base is 15 cm or so above the stream or ditch base. This may be easier if the leading edge is bevelled. Use a wooden or metal strip to protect the top edge of the sheet if you have to hammer it in. A small stilling pool is needed to slow down the flow of water immediately upstream of the weir so that the relationship between stage and discharge is not affected by changing flow paths in the ditch or stream. The pool should be at least 2 notch-lengths deep (i.e. 2 notch-lengths below the level of the notch base) by 4 notch-lengths wide by 6 notch-lengths long and it must be prevented from filling up with sediment, either by using a sediment trap or by emptying it out when it gets half full. If necessary, line the bed of the stream or ditch with a board angled away from the weir plate to prevent undercutting of the weir on the downstream side. The shape of the notch determines how accurately small discharges can be measured; the commonly-used 90o notch does not allow accurate measurement of low flows although a much narrower 20o notch has to be much deeper to cover the likely range of discharge. Discharge is low most of the time although short, sharp flood peaks occur when it is raining. Low flows need to be recorded accurately whilst not missing any of the peaks. A notch with a narrow angle at its base and a wider angle further up fulfils both requirements but makes it difficult to obtain a calibration equation from a limited number of stage and discharge measurements. The steeper the gradient of the ditch or stream, the easier it will be to use a straight sided narrow V-notch because a deeper notch can be used. Calibrate the weir by measuring both the stage and the volume of water collected in a pail in a known time period during a range of different flow conditions. This presents certain difficulties. First, a hook gauge is required to measure the water level relative to the notch base. Secondly, there must be enough room, below the notch base on the downstream side, to get a bucket or basin in to catch the water. Thirdly, a channel needs to be fixed onto the downstream side of the plate, below the notch, to allow low flows to be caught; which would otherwise trickle down the weir plate. This channel may interfere with the higher flows. Fourthly, it is difficult to be on site at the right time to catch any of the short flood peaks. During low flows, the notch tends to get blocked by debris, such as dead vegetation or insects. This leads to false readings so it must be avoided. A screen made from a suitable mesh material (for example, expanded aluminium stitched onto a fencing wire frame) should be used to minimise blockages. It needs to prevent airborne and submerged debris as well as floating material from blocking the notch. Floating and submerged debris has an uncanny ability to find its way to the notch by passing through the narrow gap between the screen and the weir plate, so fit the screen carefully to make this gap as small as possible. In order to capture rapidly changing flow levels automatic recorded is recommended. This can be achieved using pressure transducers attached to automatic data loggers.

4.3.4.2 Tipping bucket flow gauge Purpose Water usually runs off undrained bogs in small natural streams, above ground as over-land flow in very wet weather and mostly below ground as lateral seepage (see 2.5.2). On drained bogs, ditches intercept over76


Conserving Bogs

4.3

Monitoring and Site Assessment

land flow and lateral seepage so that ditchflow partly replaces these components of the water balance. If you know the catchment area of a stream or a ditch you can use the measurements of discharge to calculate what proportion of the rainfall is leaving the bog by this route. A tipping bucket flow gauge measures discharge and can also be used to monitor drainage from a natural lysimeter. Description and appraisal A bucket with an internal partition pivots on an axis running through its base. A pipe leads water from a dam and pours it from a point directly above the pivot into one half of the bucket (Figure A.19). When it is nearly full, its weight causes the bucket to tip, emptying the one half and bringing the other to the filling position below the pipe. Each time the bucket tips a magnet on one end swings past a reed switch causing it to close momentarily so that an electrical current flows for an instant. This is detected by a counter, which stores the number of tips, or by a data logger which records the time of each tip. The most advanced tipping bucket flow gauges are made of highly durable material such as Styrosun which can withstand the sun’s UV radiation, agrochemicals and extreme frost and heat. They can also encompass irrigation sensors which tip water at a preset water weight which can retain accuracy over many years. Units can be connected to a data logger that stores data to be collected when required. Additionally, many models are compatible with wireless telemetry systems. Figure 4.19 A tipping bucket flow gauge. Tipping buckets work well and are reliable provided they are well designed, carefully built and properly maintained. The pivot, in particular, must be designed not to corrode in the harsh environment of a bog ditch. Stainless steel is more resistant to corrosion then galvanised metal in these conditions. The bucket can become choked with ice in freezing weather and this causes it to tip more often than it should or to freeze up and not tip at all. Tipping buckets suitable for ditches need to hold 2-5 litres in each half and they have to be strongly built to withstand the force of the bucket crashing down with each tip. A tipping bucket designed for monitoring ditchflow costs between £800 and £1100 or can be hired for around £300 per year. A tip counter costs around £180 and is easy to use. Alternatively, record the time of each tip on a data logger (see 4.3.3.6). Method  Measure the height of the central partition above the ground when it is at the half-way position (i.e. directly above the pivot).  Also measure the height of the lowest point of the emptied bucket above ground.  When damming the ditch, use the first measurement to indicate how much clearance is needed between the outlet pipe and the ditch base on the downstream side. You can dig out the base slightly; the second measurement tells you how high the water level can be above the base before preventing the bucket from emptying.  Arrange the outlet pipe of the dam at the lowest level that allows the tipping bucket to work properly. This minimises the extent of ponding of water above the dam, thus minimising evaporation from the ditch.

77


Conserving Bogs

4.3

Monitoring and Site Assessment

 Install the tipping bucket with its pivot directly below the end of the outlet pipe and level it so that both halves of the bucket fill to the same level. Make sure the water from the pipe only enters the half of the bucket in the filling position and that the bucket partition does not touch the pipe when it tips. Two types of calibration can be used: static and dynamic. Static calibration involves temporarily blocking the outlet pipe from the dam or extending it to take the water down past the tipping bucket. Each bucket is filled slowly using a one litre measuring cylinder and the volume needed to make it tip is recorded. The mean of the two sides can be used later to convert the number of tips to a water volume. Repeat this calibration at regular intervals. During floods, water may be gushing out of the pipe so fast that a substantial volume goes into the bucket between the time it starts to tip and the time it reaches the half-way position. In these conditions, the buckets hold more water than the amount measured, thus underestimating the discharge when using the static calibration. This underestimation is small enough to be unimportant for most purposes although when monitoring discharges very accurately, it is advisable to use a dynamic calibration. Data analysis, display and interpretation Use the calibration to convert the number of tips in a period to a water volume. Given an estimate of catchment area of the ditch or stream, divide the total volume in litres by the catchment area in square metres to give the run-off in millimetres. Display the period discharge measurements using a bar chart. Use unshaded bars to display a series of weekly, fortnightly or monthly rainfall and shade the lower part of the bar representing discharge. Figure 4.20 The relationship between the measured water level (x) and the discharge (y) can be obtained using a calibration line. 4.3.4.3 Piezometers Stage boards, V-notch weirs and tipping bucket flow gauges all measure discharge in discrete ditches or streams. Measuring seepage through the peat is achieved by using piezometers which can them be used to calculate hydraulic conductivity. Piezometers are similar to dipwells except water only enters through the base of the tube. They can be bought or made easily from 52mm internal diameter PVC pipe or 2" plastic waste pipe. To stop peat filling up the pipe from the base, cover the base with ladies tights (or gauze) and affix with tape. To measure the rate and direction of seepage towards a cut face, an array of piezometers is required.  Mark out a line at right angles to the face and mark two points on this line, 1m and 5m from the face.  At both of these points install a group of piezometers at 0.5m depth intervals down to the level of the base of the cutting. Within a group, install the individual pipes 20cm apart in a line parallel with the cutting.  The pipe must be a tight fit with no gaps along the outside. To achieve this, push the piezometer straight into the ground, rather than into a ready made hole. A 10 cm length protruding above ground and a coloured cap on top will make it more visible.  The piezometers are read with a dipstick and the depths to water recorded.  At some time during the monitoring period measure the height of the ground surface at each piezometer relative to a fixed datum point, such as the top of a firm post, using an automatic level, if available, or by careful use of a straight edge, a spirit level, a plumb line and a tape measure. Calculating seepage rates and exact directions from piezometer measurements is complicated and should be done by an expert. However, a rough idea of the direction of water movement can be obtained by using the 78


Conserving Bogs

4.3

Monitoring and Site Assessment

rule of thumb that water moves from areas with a high pore water pressure towards places with a lower pressure. For example, water is likely to move from an area with a nest of piezometers showing high waterlevels to an area with a nest showing lower water-levels. Automatic data loggers can be used to collect data at a higher frequency and software packages and some free spreadsheet tools are available to enable the calculation of hydraulic conductivity. These may however not yet be suitable for application to peat (adapted from Bonnett et. al 2009).

4.3.5 Evapotranspiration – Lysimeters Purpose Evapo-transpiration rates are markedly different on undisturbed and disturbed bogs. More natural bogs, dominated by Sphagnum mosses, exhibit low evapotranspiration rates as Sphagnum lawn and hummocks have tightly-packed capitula at the surface. Under dry conditions, Sphagnum wilt to a white colour reflecting heat. Vascular plants, which characterise more disturbed bogs, have higher transpiration rates and can dry a bog further. Monitoring evapo-transpiration rates requires the use of a lysimeter. Description and appraisal A lysimeter consists of an area of representative vegetation and underlying peat which is isolated from its surroundings by a waterproof barrier which prevents lateral seepage (see 2.5.2) into and out of the area. Small lysimeters are sometimes constructed by cutting out a block of peat with the surface vegetation and fitting it tightly into a container such as an oil drum or plastic tank with an outlet pipe and some means of monitoring the discharge from it. It is normally used in conjunction with a rain-gauge and a few dipwells so that evapotranspiration can be estimated by subtracting the total seepage, as indicated by the outlet discharge, from the rainfall and a correction can be made for any change in the amount of water stored in the peat as indicated by a change in the dipwell water level. One type, known as a weighing lysimeter, has a built-in weighing device, so that the amount of water in and on the soil and vegetation can be monitored accurately. A natural lysimeter has no artificial lining below but uses an impermeable peat or clay layer to minimise vertical seepage. A tipping bucket or a pipeflow gauge based on a V-notch weir built into a weir box are alternatives for measuring the discharge from the outlet pipe. Lysimeters are difficult to construct. A successful lysimeter must measure total seepage without affecting evapotranspiration. Except in very small lysimeters, it is usually not possible to seal off the underside although, where the waterproof barrier around its edge reaches down to an impermeable layer, this is adequate. Avoid disturbing the vegetation and make sure the lysimeter does not lower the water-table below its previous level otherwise the measurements are atypical and worthless. Method  Decide on the size of lysimeter you need. Ones less than 1 m2 in area have been used in uniform vegetation while others of 5 ha have been used in mature conifer plantations. The scale of variation of most bog vegetation dictates a size in the range 10 to 20 m2 although it may have to be larger (up to 100 m2) if there are trees or tall shrubs because the scale of variation of these types of vegetation is larger.  Choose a fairly flat area with vegetation typical of the surrounding bog. It helps if there is a slope leading to lower ground nearby so that the outlet pipe can lead water to a place where there is at least a 40cm fall the minimum necessary to install a suitable discharge measuring device.  Mark out the lysimeter area; it can be circular, oval, square, rectangular or any regular shape.  If the peat beneath the fibrous surface layer is pseudofibrous or amorphous or shallow and overlies heavy clay, dig a ditch right round your lysimeter area which is deep enough to reach this layer.

79


Conserving Bogs

4.4

Monitoring and Site Assessment

 Use a blunt-edged board to push a waterproof barrier, such as a doubled over sheet of thick polythene, into the centre of the ditch base. In the clay layer (or well humified lower peat), dig a narrow trench, insert the barrier and backfill with clay, stamping it well down to form a seal.  Carefully seal the ends together where they meet, using a water resistant sealant, and strengthen this joint. Fill in the ditch evenly on both sides of the barrier, stamping the peat down to fill up any air spaces.  If the peat is relatively undecomposed and therefore fairly permeable, dig out blocks of peat complete with vegetation from the lysimeter area and replace them after lining the hole with a waterproof barrier such as a sheet of thick polythene.  Make good the surface afterwards and if the vegetation shows any signs of suffering from the disturbance, allow a period of a few weeks for it to recover before starting monitoring.  From knowledge of the site or from previous dipwell readings, estimate how far below the surface the water table lies during the winter. Make a hole in the barrier at this depth and seal a pipe onto it to lead water away to the discharge measuring device.  Install four or five short dipwells, within the lysimeter, taking care not to puncture the barrier if you have laid one as a base. A more detailed description of the design and use of a lysimeter is given by Calder (1976). Data analysis, display and interpretation Calculate weekly or daily evapotranspiration by subtracting the outlet discharge plus the increase in the peat water store from precipitation. An example is shown below for a lysimeter covering 16m2 over 1 day Step 1 Convert outflow (U) (measured in a tipping bucket gauge) to millimetres depth. Average tip of 0.261litres. Number of dips in a day = 174 Volume = 174 x 0.261 = 45.4l Outflow = 45.4l divided by 16m2 = 2.84mm Step 2 Calculating change in water store(W). Four dipwells - average rise of 3.25cm. Use a conversion factor (below) to calculate change in peat water store. Peat type Factor % pore space Undecomposed, 0.3 33 surface Fibrous 2.0 5 Well humified 5.0 2 Factor of 2.0 used: 3.25 divided by 2.0 Change in peat water store = 1.625mm Step 3 Calculate daily rainfall (P) Rain gauge showed 5.5mm of rainfall Step 4 Calculate evapotranspiration (E) Note, vertical seepage (G) = 0 Use the water balance equation (see 2.5.2) E = P - U - G - W 1.035 = 5.5 - 2.84 - 0 - 1.625 Evapotranspiration = 1.035mm For a pipeflow gauge, use its weir calibration equation to convert the series of stage readings to discharge rates. For each period multiply the mean discharge by the time interval and sum the volumes in litres before finally dividing by the lysimeter area. 80


Conserving Bogs

4.4

Monitoring and Site Assessment

As well as evapotranspiration, the most advanced lysimeters can measure drainage rates, collect water samples for biochemical analysis, measure percolation rates and calculate water balance. Many have inbuilt water sensors and can be connected to data loggers and GPS modem for data storage. Ventilation chambers can be used to directly measure evapotranspiration by enclosing vegetation in chambers and comparing rates of evapotranspiration between different vegetation types.

4.4 CHEMISTRY 4.4.1 Introduction and Sampling The acidic and nutrient poor nature of bogs makes them very sensitive to pollution of any sort (see Section 2.6, 1.13, A3.7.1). Chemical analyses should be considered when for example:  pollution is suspected;  water is being directed or redirected onto the bog surface;  the potential of restoring cut-over bog is being examined. Hydrological changes also bring about chemical change by oxidation and mineralisation of dry peat. A bog's chemical environment is partly indicated by measuring acidity (pH) and conductivity for which cheap and easy to use hand-held measuring devices are available. The pH of bog waters is generally between 3 - 4.5 whilst conductivity is generally less than 100 S. Different figures would suggest there may be a problem. A more definitive description of bog chemistry is derived by measuring other variables: cations, anions, dissolved organic matter and redox potential; these are more difficult to analyse and often have to be carriedout in a laboratory. Nitrogen and phosphorus are useful variables to measure as they indicate soil fertility. If samples are to be sent to a laboratory, they have to be collected carefully. Chemical data expressed by dry weight (gravimetric samples) are easy to collect as compaction and/or expansion is not a problem. Where analyses are expressed by volume (volumetric samples), the samples need to be collected and stored so as not to affect its bulk density. Samples collected for mineral or gross organic determination (e.g. calcium, carbon, nitrogen, sulphur etc.) can be stored in metal or plastic bags, tubes or boxes. If organic components are to be analysed (e.g. pesticide residues), only metal or glass containers can be used. For surface water analyses, waters should be stored in completely filled (avoids oxidation) 300 ml polypropylene bottles and stored at 2-5ºC in a refrigerator (never frozen).

4.4.2 pH pH is simply a measure of how acid or alkaline a sample is. Technically, pH = -log10[H+], where [H+] is the concentration of hydrogen ion in aqueous solution. It is commonly measured using electrochemical meters. The meter probe is inserted into the sample, into wet peat or into peat mixed with de-ionised water. Remember to calibrate the meter using standard solutions before use. The literature accompanying the pH meter and the standard buffer media explain the procedure in detail. Water samples should be measured with a temperature compensation allowance, that is, with the solution temperature compensated by measuring the pH of a standard at the same temperature (carry your field standards externally in a poly-bag, if using battery-powered equipment), or by the inclusion of automatic temperature compensation within the pH meter. Modern portable and laboratory pH meters are fully temperature-compensated with a temperature thermistor included in the electrode array. This feature can Watch the readings and be aware of slowly downward-drifting results when analysing samples which are likely to contain a lot of iron or aluminium. Glass electrodes are usually designed to measure pH in solutions of conductivity of >100 S cm-1 but certain water samples for example, rainwaters or upland waters, may be below the limit. Low conductivity electrodes are available and must be used if these low conductivities are encountered and an accurate pH measurement is required. 81


Conserving Bogs

4.5

Monitoring and Site Assessment

be useful in determining sample temperatures and electrode performance (see ion-selective electrodes below). Soil pH values ( or soil reaction) are normally measured by mixing soil and de-ionised or distilled water in 1:4 proportions for air-dried organic soils such as peats. Since dried peat is usually difficult to re-wet, measurement of pH is best made using field-moist peat samples, in a moist peat:water ratio of 1:2. Note that, pH values in intact peat cores may be up to 0.5 - 1.0 units less than those seen in suspensions. This is due to the dilution effect of mixing a sample with water.

4.4.3 Conductivity The measurement of electrical conductivity in water samples gives a measure of their content of ions and can be performed in the field using equipment similar to pH meters. In peat surface and drainage waters, this determination can give indications of the incursion of unwanted inorganic components perhaps derived from adjacent agricultural land, of mineral groundwater or sea-salt contributions. The determination is simple and is usually performed in conjunction with pH measurements. Conductivity is temperature dependent so if conductivity measurements are required, buy a combination pH, conductivity and temperature metre. Several field meters are available for the simultaneous measurement of pH, temperature and conductivity; these also usually have a mV mode which allows the measurement of redox potential and ionic strengths (for selective ion determinations). These are very useful meters in situations which require detailed monitoring of water quality. Redox potential, for example, is considered to be an important variable when monitoring the burial environment of in-situ archaeological remains since it gives an indication of aerobic/anaerobic conditions.

4.4.4 Redox potential Redox potential is a measure of the tendency of a chemical species to donate electrons (reduce) or acquire electrons (oxidise) any reducible or oxidisable substance. Evidence in the literature shows that the restoration of peat-based wetlands by reflooding can induce the redox mediated release of soil nutrients thereby increasing the risk of diffuse water pollution (Niedermeier & Robinson, 2007). This may be important when making management decisions. To measure the redox potential, a platinum electrode is connected to an mV meter. Many pH meters also have an mV scale. It is most convenient to use a combined platinum KCl electrode. Tables are available to relate the oxidation-reduction potential Eh to the ion forms of interest, but redox alone is a useful index of the extent of oxidation or reduction in the system (Jones & Reynolds, 1996; Mitsch & Gosselink, 2000, Bonnett et. al 2009).

4.4.5 Laboratory Techniques There are many techniques used for analysing chemical constituents. A few are shown in table 4.2 below: Technique X- ray flourescence Total Nitrogen by digestion Gas chromatography Plasma spectrometer Ion exchange chromatography Flow injection analysis Oxidation/combustion

Analyses Ca, Na, K, Mg, Fe, Al, Si, Mn, S, P, Cl in a single analysis N C, H, N Ca, Na, K, Mg, Cu, Zn, Mn, Fe, Al, Si, S, P in a single analysis Cl, NO3, SO4 NH4, PO4 Dissolved organic carbon

Table 4.2 Techniques for analysing chemical constituents of peat.

82


Conserving Bogs

4.5

Monitoring and Site Assessment

4.5 PEAT 4.5.1 Introduction The inextricable links between the peat, water and the vegetation means that it is important to look at the peat itself. Knowledge of peat depth, peat surface level changes and some idea of the peat properties can be useful supplementary information for managers. Such information, for example, would be important to assess the likely success of rewetting peat fields. Shallow depths of poorly-humified peat could lead to high vertical seepage losses making rewetting schemes impossible. This section describes how to measure peat depths (see 4.5.2) assess changes in surface levels (see 4.5.3) and sample peats (see 4.5.4) In addition, a brief description of the main methods for assessing seven of the most important peat properties is given (see 4.5.5). This can be specialist work and land managers are advised to consult more specialist texts, seek advice from specialists. Methods for monitoring peat erosion are also briefly mentioned. (This widespread occurrence has yet to be managed successfully (for example, Phillips et al 1981), although there has been much research work).

4.5.2 Peat Depth Where peat overlies mineral ground directly, peat depth is easy to assess. Interlocking rods (linked with bayonette connections (Figure 4.21) or screwed together) are simply forced through the peat until the underlying firmer mineral ground is reached. For peats overlying lake basins (many raised bogs for example), the peat/sub-surface boundary is more difficult to gauge. With experience the ‘feel’ of rods pushing through the sediment can indicate when a different material from peat has been reached. However, to be really sure, peat should be sampled (see 4.5.4). Difficulties are also encountered where the peat is woody, in these cases; it is useful to attach a screw auger to wind through soft wood.

Figure 4.21 A Metal rods can be used to measure the depth of peat. The rods can be inter-locked using bayonet connections.

83

Figure 4.22 Taking peat depth measurements In the Yorkshire Dales.


Conserving Bogs

4.5

Monitoring and Site Assessment

Ideally, augering positions should be levelled (see 4.2) to allow absolute sub-surface heights to be plotted. In some situations (where the underlying sediments and the peat are very different), peat depth can be ascertained using radar and seismology. 4.5.2.1. Ground Penetrating Radar (GPR) Peat depth can also be ascertained using Ground Penetrating Radar (GPR). Measuring peat depth using GPR is now a commonly deployed method to accurately measure peat thickness and the presence of sub surface peat pipes. GPR emits short pulses of electromagnetic energy transmitted by an antenna through the ground surface and reflected from boundaries between layers or from internal irregularities which have differences in electrical properties. Reflection is detected on the surface and the time between transmission and detection is proportional to depth (Holden et. al. 2002). Lower frequency wavelengths are used to measure increased depth whilst higher frequency wavelengths are generally used to detect sub-surface soil pipes. Transects are set up across the peat system and measurements are made at regular intervals in order to build a cross-section of peat thickness. GPR units can be fixed to low level air craft, mounted on low ground pressure track vehicles for large-scale, lower resolution studies or used manually to generate high resolution data. Using GPR to measure peat thickness is now common practice as accuracy improves and costs reduce. Conducting GPR surveys and interpreting GPR traces requires a high level of expertise. See figure 4.23 for an example of the traces generated by GPR.

2.

1.

4. 3.

Figure 4.23 Processing and interpreting traces generated by GPR. 1. 2. 3. 4.

Traces are processed in order to allow for the depth and peat pipe interpretation. Ground surface, peat surface and peat piping interpreted. Schematic 3D diagram showing pipe picks (circles) from GPR data. Pipe picks in 3D are projected onto a 2D cross section of elevation (y) and down slope distance (x).

84


Conserving Bogs

Monitoring and Site Assessment

4.5.3 Surface Level Changes

4.5

The surface level of a peat bog can change. This is because peat is mostly water, so changes in water content affect the height of the column of peat. Effective drainage schemes can, for example, cause a peat surface to drop by half. Commonly the surface levels change between winter and summer - a phenomenon known as mooratmung or ‘bog-breathing’. Peat anchors are used to detect changes in the fall or rise of the bog surface or to detect peat accumulation over many years. Wood or metal (such as gas pipe) can be used but wood is suitable only for shallow peat and is more easily dislodged by frost and animals. Metal conduit pipe is generally suitable:  Prime and paint (for example, Hammerite) metal conduit pipe to protect it from corroding or to protect the bog from zinc pollution if the pipe is galvanised (non-galvanised pipe is available).  Determine peat depth using depthing rods (see 4.5.2).  Cut an appropriate length of conduit.  Push through peat until the underlying mineral ground is reached, then with a sledge hammer, or similar, drive into mineral ground until the pipe is secure.  The pipe protruding above the surface of the bog can be protected with a capped length of u-PVC fall pipe. A protrusion of 30 to 50cm is adequate.  Measure from top of conduit to bog surface, using a ruler or a collar and ruler. It is sometimes confusing to work out exactly where to measure to the surface. Measuring to the top of a Sphagnum carpet (where available) is probably best. A slightly more sophisticated versions are used at some sites for example, Cors Caron and the South Solway Mosses. Figure 4.24 Design details of the anchor posts used to measure the rise and fall of a bog (adapted from a design by J. Davis, CCW). Rise and fall of the bog is measured in two ways; 1. By measuring the top of the anchor post to the top of the anchor plate post. 2. By making a saw cut in the anchor post at the top of the anchor plate. 4.5.3.1 Accumulation plates Peat accumulation can be measured by inserting a metal plate just below the peat surface relative to a datum post fixed into the underlying mineral substratum. The top of the fixed datum will remain the same and peat depth measurement can be taken from surface of the bog to the metal plate. Changes in peat depth will reflect peat accumulation or peat loss. The height difference between the fixed datum and the metal plate will also provide an assessment of peat swelling if measured on a regular basis. The metal plate can be relocated using a metal detector or ideally recorded using a GPS device. LIDAR and high resolution aerial imagery can be used in combination with GIS to generate detailed surface topography data. If this imagery is generated sequentially, surface level changes may be accurately recorded. 85


Conserving Bogs

4.5

Monitoring and Site Assessment

4.5.4 Sampling Peat Before peat properties can be assessed it needs to be sampled. To sample peat at depth there are a variety of coring devices available. Shallow peat can be sampled with a spade or a section of drainage pipe. The commonest devices are shown in Figures 4.25, 4.26 and 4.27. Peat cores from these corers provide a rich and neatly stacked archive of cultural and environmental information (see 1.6) and are commonly used; they can often be borrowed from university environmental departments. Alternatively they can be specially made or bought commercially.

Figure 4.25 A Russian corer provides a half cylinder of peat. Compaction is minimal and the sampler is easy to use (Julia McCarroll).

Figure 4.26 A box corer is simple to use, the front has been removed to show the sample (Andreas Heinemeyer).

Figure 4.27 A peat core taken from Oxenhope Moor in the South Pennines as part of PhD study investigating how paleoecological techniques inform mire and moorland conservation (Julia McCarroll).

4.5.5 Peat Properties 4.5.5.1 Degree of Decomposition or Humification The level to which plant material decomposes during peat formation affects other properties such as bulk density, water storage capacity and hydraulic conductivity. In ombrotrophic peats, the degree of decomposition or humification also relates to how wet the bog was during peat formation and hence prevailing climatic conditions (Barber 1981). Various methods are used to assess humification, the first is the Von Post method, which assesses a humification or H-scale running from H1, undecomposed peat, to H10, completely decomposed peat, based on a number of diagnostic features and criteria (see Table 4.3). The steps required for Von Post assessment are as follows (with reference to Table 4.3): 86


Conserving Bogs

4.5

Monitoring and Site Assessment

 Sample the peat (using a Russian-type, gouge or box sampler, grabbing a handful and so on).  Inspect peat for changes in colour, texture and so on and note or mark the depths at which changes occur.  Take a piece of peat, break and inspect the fresh surface to confirm above observations and observe the nature and proportion of identifiable plant remains (Table A3, column 3).  Squeeze the peat slowly and gently and observe whether water is extruded out and the colour of the water (Table A3, column 1).  Squeeze firmly and observe whether peat is extruded between fingers and the proportion of the sample that is extruded (Table A3, column 2).  Rub a small amount between forefinger and thumb to determine the texture (Table A3, column 4).  Compare the proportion of identifiable plant remains before and after the peat is squeezed and rubbed (Table A3, column 3 and 5).  With reference to Table 4.3 assign an H-value to the sample. 4.5.5.2. Peat Texture Peat texture gives a rapid indication of the type of peat present at each site and to some extent the possible degree of peat degradation. It is a useful proxy measurement for peat. A quick assessment can be made using the following series of questions; Q1. Is the soil very black, loose and with a low density? Yes = Peat, No = Q2 Q2. Is the soil grey to black; does it bind to form a ball? (Soil may be granular) Yes = Q3, No = Q4 Q3. Is the soil also sandy? Yes = Sandy peat, No = loamy peat Q4. Is the soil grey; does it bind to form a ball that holds together firmly and feels smooth? Yes = Peaty loam, No = Q5 Q5. Is the soil dark coloured but the mineral component dominant? Yes = O-rich other soil, No = other soil 4.5.5.3 Fibre Content Method A number of methods have been devised for assessing the degree of decomposition in terms of the fibre content of peat. The fibre content is expressed as a percentage of volume or of dry weight of peat. The system devised for the United States Department of Agriculture (Lynn, McKenzie and Grossman, 1974) and is summarised below:  Sample peat using an appropriate sampler.  If peat has dried in the field, soak samples for 24 hours.  Remove excess water by rolling in paper towels.  Pack a 5 ml syringe that has been cut in half longitudinally, with the peat. Compact sample just enough to force air, but not water out of the sample. 

ear.

 Blot sample and repack in the syringe.  Read the residue volume and record as a percentage unrubbed fibre.  Return residue to the sieve and rub between thumb and forefinger in running tap water until the effluent is clear.  Repeat blotting and repacking process and record volume as percent rubbed fibre. Additional methods for determining fibre content have been developed; the USSR centrifugation method uses a series of different sized filters to compare the total volume of the peat sample and the volume passing 87


Conserving Bogs

4.5

Monitoring and Site Assessment

through the filters and the ASTM fibre method involves soaking a peat sample in a dispersal agent then passing it through a filter (Malterer et. al., 1992).

Principle diagnostic features Nature of Proportion liquids Nature of Decomposition extruded expressed plant Texture state between on residues fingers squeezing Clear, colourless

None

Unaltered

Almost clear yellowbrown Slightly turbid brown

None

Plant structure distinct

None

Plant structure distinct; most identifiable

Turbid brown

None

Strongly turbid, contains a little peat in suspension

Very little

Component fragments distinct; leaves identifiable Plant structure clear but becoming indistinct

One-third

Plant structure indistinct

One-half

H7

Dark brown, much peat in suspension Strongly muddy

Two-thirds

H8

Thick mud, little free water

No free water

Nearly all

H9 H10

No free water

All (unless too dry)

Indistinct with few remains identifiable Very indistinct, only plant fibres and wood identifiable Plant structure almost unrecognisable Completely amorphous

H1 H2

H3

H4

H5

H6

Description

Very rough, and very spongy Very rough, and spongy

Undecomposed

Moderately rough, slightly spongy, moulded residue when squeezed Very slightly soapy feel; moulded residue Slightly soapy feel. Moulded residue

Very weakly decomposed

Moderately pasty, moulded residue Very pasty, moulded residue

Well decomposed

Comments

Living or recently dead

Almost decomposed

Weakly decomposed

Moderately decomposed

Unsqueezed peat may appear to have greater proportion of identifiable remains than expected.

Strongly decomposed Very strongly decomposed

Feels greasy

Feels very greasy

Almost completely decomposed Completely decomposed

Table 4.3 Assessment of humification based on the Von Post scale.

4.5.5.4 Calorimetric Method The colour intensity of an extract of an aqueous alkaline solution of a peat sample relates to humification (Aaby and Tauber, 1974). The simplest method is used by the U.S. Department of Agriculture: 88


Conserving Bogs

4.5

Monitoring and Site Assessment

 Take a 2.5 ml sample (fibre content method).  Add 1g of NaP2O7 crystals to 4 ml of water, add peat and stir.  Stand for one day.  Restir and insert one end of a strip of chromatography paper (0.5cm x 3.0cm) until all of the strip is moistened.  Compare colour of the paper with a standard Munsell colour chart. More complex quantitative methods are described by, for example, Aaby and Tauber (1974). Humification values are often plotted against depth forming proxy-climatic curves (for example, Blackford, 1993). A revised system for the European wide ACROTELM mire-based palaeoclimate project (Chambers 1996) has been developed which uses percentage light transmission values rather than absorbance data, see Chambers et. al., 2010/11. 4.5.5.5 E4:E6 ratio E4:E6 ratio ((ratio of humic acid (E4) and fulvic acid (E6)) is commonly used to measure rates of humification in peat. It is determined by filtering samples through 0.45 µm filters and measuring absorbance at 465 nm (E4) and 665 nm (E6) on a spectrophotometer (Jonczyk et al., 2009). More complex humification estimates using multiple parameters have also been developed McMorrow et al. (2004) reports on progress towards using HyMap data at 3m spatial resolution and laboratory spectroradiometry to estimate physico-chemical properties of exposed peat, notably the degree of humification (Bonnett et. al 2009). 4.5.5.6. Peat colour: The colour of the peat itself can be used to determine to a certain extent its composition. The colour of peat is determined by the following factors; 1). The presence of soil organic matter. Organic matter imparts a dark brown to black colour to the soil. As a general rule, the higher the organic matter content the darker the soil. 2). The oxidation status of the iron compounds in the soil. In more drained and aerated soils Fe (III) minerals give soil a red or yellow colour. In poorly drained soils, iron minerals are reduced and neutral grey coloured minerals predominate. PEAT COLOUR Colour is assessed using the Munsell Soil Color Chart. Colours shown below are from Hue 7.5YR. RGB values are given to help with accurate colour printing reproduction.

4.5.5.7 Water Content Water-level readings can be supplemented by calculating the water-content of peat. In natural catotelmic peat (lower, saturated peat), water content is commonly 90-96% of fresh weight of peat. Occasionally, water content is expressed as % of dry weight in which case values of 1,800-2,400% are typical. The assessment procedure is as follows:  Remove a core of peat from the site (see 4.5.4).  Place the full sampler horizontally on the bog surface before opening the chamber to minimise water loss. 89


Conserving Bogs

4.5

Monitoring and Site Assessment

 While peat is still in the chamber, cut samples into appropriate depth increments and place in sample cans or polythene bags. Use at least two bags as welds can fail.  Express air from bags and seal (fold top over and wrap an elastic band around folded top or if bags are large enough close with a knot).  Keep sample as cool as possible.  Weigh sample as soon as possible.  Oven dry at 90oC until weight is constant.  Weigh sample.  Calculate water content: % fresh weight =

% dry weight =

Fresh weight - Dry weight x 100 Fresh weight Fresh weight x 100 Dry weight

Time domain reflectrometry (TDR) has been regularly used to measure water content in peat soils, based on measuring the reflection time of an electromagnetic pulse. GPR can also be used to generate accurate estimations of peat water content.

4.5.5.8 Bulk density Bulk density is a measure of the dry weight per unit volume of fresh peat. Shrinkage of peat in response to drainage or erosion increases its bulk density. Procedure for determination is as follows:  Cut peat, while in sampler chamber, into incremental lengths and place in sample cans or polythene bags (see water content methods).  Weigh fresh peat samples.  Oven dry samples to a constant weight (700C – 1000C, 2 – 3 days).  Bulk density = Dry weight (grams) Volume of sample (I, ml or cm3) Bulk density can also be measured using GPR (Parry et. al., 2012) and the Environment Agency have also flown low level flights to determine peat density using GPR (Bonnett et. al 2009). Time domain reflectrometry (TDR) and amplitude domain reflectormetry (ADR) are methods based on estimating the volumetric water content. Probes are used to measure changes in peat water content which are then used as to calculate bulk density, this is a relatively fast and cheap way to determine bulk density. For more information see Wijaya et. al., 2003. 4.5.5.9 Ash Content The ash content is the mineral residue that remains when peat is combusted. It consists of atmospheric and ground-water borne mineral inputs and the mineral components of plants. Bog peat has a low ash content which mostly ranges from less than 2% to about 5%. The value can be affected by the degree of decomposition of the peat but high values generally indicate a ground water input at the time of deposition. Procedure for estimation is as follows:  Oven dry and mill or grind sample (use a coffee grinder).  Re-dry sample and place a weighed (weigh to two or three decimal places) sub sample of approximately 0.2g in a crucible.  Place in a furnace at 500oC to 600oC and leave for 24 hours. 90


Conserving Bogs

4.5

Monitoring and Site Assessment

 Weigh residue.  Calculate ash content as a percentage of oven-dry peat: Ash Content = Weight of ash residue x 100 Weight of oven dried sample 4.5.5.10 Carbon content The total amount of carbon in peat is quantified as the product of bulk density (g cm -3) and total carbon content (gravimetric %) of the material (Chambers et. al. 2010/11). Quantifying the current carbon pool and quantifying changes in carbon over time can provide evidence on the success of restoration techniques. Total carbon is commonly determined in peat by dry combustion and elemental analysis. Organic carbon can be measured by dry combustion after removing carbonates by acidification. Inorganic carbon (IC) can be quantified indirectly as the difference between TC and OC ((Busuitti et. al. 2004) Chambers et. al. 2010/11). 4.5.5.11 Botanical Composition It can be useful to study the composition of the peat - the semi-decomposed remains of the plants which formed the peat. These remains reveal much of the site’s past history: its development, the pre-interference vegetation and the effect of certain events, for example. In bog peats, there are few different types of vegetation: Sphagnum, sedges and ericoids are most common. The main components are shown in Table 4.4.

Table 4.4 Description of principal botanical components Sphagnum

In peat of low H-value almost entire, clearly observable plants may occur. In moderately decomposed peat, stems and leaves are usually separated. Sphagnum leaves (Figure 4.16) are characteristically boatshaped.

peat samples. Scirpus cespitosus (deer sedge) bases and rhizomes are occasionally found but are difficult to distinguish from undifferentiated sedge remains. Of the grasses only purple moor grass (Molinia caerulea) is a feature of bog peat and then usually only in very high rainfall areas. It has a characteristic swollen leaf base and an irregularly shaped rhizome with leaf base scars. The roots are twisted pale coloured and up to 2 mm broad.

Mosses (excluding Sphagnum)

In bog peat very few mosses besides Sphagnum are identifiable in the field. The commonest are Polytrichum (P. commune and P. alpestre) and Racomitrium lanuginosum (wavyhair-moss). Polytrichum remains usually occur as thin mats of dark stems on which at least a few leaves of several mm length remain. In the northern maritime and high altitude bogs of Scotland, R. lanuginosum can be a peat-former. In such situations, R. lanuginosum is usually abundant in the present vegetation. In the peat it appears as a crushed or compacted mid-brown version of the living plant. A hand lens clearly reveals this resemblance.

Woody structures Small quantities of fine twigs and

roots occur in most bog peat samples. They are mostly the remains of ericaceous plants and particularly ling heather. Cross-leaved heath and cranberry may also occur. A somewhat twisted, irregularly and sparsely pitted and striated twig is characteristic of ling heather. Crossleaved heath twigs are generally straight and the rings of leaf scars may be visible. Cranberry twigs are fine (approx. one to two mm diameter) and wiry. Roots are rarely distinguished and are generally categorised as ericaceous roots. Birch twigs and roots may occur. They have a smooth and shiny bark. Occasionally alder, willow and pine is found. The bark of alder and willow may also be shiny and hence difficult to distinguish from the commoner birch.

91


Conserving Bogs

4.5

Sedges and grasses

Monitoring and Site Assessment Two species of cotton grass are commonly found in peat, namely E. angustifolium (common cotton grass) and E. vaginatum (hare’s tail cotton grass). Both shoot bases and roots can be identified. The shoot bases are fibrous but those of common cotton grass mostly occur singly whereas those of hare’s tail cotton grass are generally clumped. The shoot bases of the latter species are generally stronger and more resistant to breakage when handled. Some of the roots of common cotton grass and hare’s tail cotton grass are pink and black respectively in freshly exposed

Fruits and Seeds

These are only occasionally found. Those that are one or two mm long, trigonous or elliptical with a break are usually Cyperaceae (sedge family) fruits or seeds. Carex (sedge), Eriophorum, Scirpus and Rhynchospora are the main genera found. Elongated bean shaped Potentilla erecta seeds up to 2 mm long with undulating ridges are occasionally found. More frequently, rounded bean shaped Menyanthes seeds up to 3 mm across occur in peat deposited in or around former wet hollows.

Figure 4.28 Identifiable Sphagnum leaves from moderately decomposed peat can identified to section level on the basis of their shape. For more details see Daniels and Eddy (1990) and Hill (1992).

4.5.6 Peat Erosion 4.5.6.1 Introduction To date, most erosion investigations have been carried out to determine the rate of surface lowering and to find out how rapidly peat erosion features develop. This has yielded useful insight into the age and persistence of erosion features. For example, Birnie (1993) found that peat erosion was progressing at the rate of 1-4cm per year suggesting that the peat landforms in Shetland would persist for between 30 and 150 years depending on peat depths. Reports of upland catchment surface peat erosion range from 5-45 mm a1 (Evans and Warburton 2007). However, from a management perspective, it is probably more critical that a monitoring programme is linked to a programme for assessing the effectiveness of alternative management regimes for re-instating damaged peatlands or for controlling further erosion (for example, exclusion of large herbivores). 4.5.6.2 Methods Assessing quantity and rates of peat erosion can be approached through the use of reference markers, mapping and estimating the sediment resulting from erosion. The use of reference markers involves pushing thin (1-10 mm) erosion pins or rods into the peat or, in shallow peats, through to the mineral ground. The pins should be surveyed and then the amount protruding above the ground measured at appropriate time intervals. Another way to achieve similar results is to bridge two pegs with a point quadrat frame and measure the distance between inserted needles and the peat. The area of erosion or differing erosion patterns can also be mapped. This data can be used in conjunction with reference markers to assess the quantity of peat eroded and provide information about the rate of spread/retreat or lateral expansion of erosion systems. Of the methods outlined, plane table mapping and a simple line survey (measuring along tape measures the distances where erosion occurs) are most appropriate. Aerial photography (see 4.6.6.1) can also be used to map erosion features and systems. Tallis (1981) describes a method to calculate the rate of peat erosion by comparing aerial photographs taken on different dates. 92


Conserving Bogs

4.6

Monitoring and Site Assessment

High resolution satellite imagery, LIDAR and aerial photography derived DEM’s combined with GIS software can be used to quantify peat erosion and loss using sequential imagery. A proxy method of measuring erosion rates is to measure the amount of sediment arising from erosion (bearing in mind that wind and oxidation also removes peat). Sediment can be trapped using screens of different mesh sizes (e.g. Tallis, 1973) and then dried and weighed. The quantity of sediment trapped by reservoirs in upland catchments have also been examined (Ledger et al., 1974; Tallis, 1981) to determine peat erosion rates. Sediment traps measure the transfer of material across the peat face (Evans and Warburton 2007).

4.6 VEGETATION 4.6.1 Introduction Conservation management of bogs is often undertaken to change vegetation composition and structure. This is achieved by direct methods of vegetation management (see 5.3-5.5) or indirectly by modifying hydrology (see 5.1). Whatever, the effects of such management can be ascertained by monitoring vegetation. The techniques are common to many habitats so only a summary is provided here. Prior to embarking on vegetation monitoring schemes, the study area should be defined. It may be the whole bog, or a representative part of a bog, in which management is to take place, or has taken place. Whole site assessment can be achieved through the use of aerial photographs (see 4.6.6.1) although this approach is not necessary on small areas or small sites. A different approach uses representative plots chosen for monitoring. Important considerations include:  Should the plot be unfenced or fenced to stop monitoring equipment getting damaged by animals and/or to monitor the effect of grazing?  Plots often need to be relocated - reference markers or obvious features are used for guidance.  Monitoring itself may affect the plot confusing the results.  What species should be monitored - all or a representative set of indicators?  If representative plots are chosen (usually quadrats) do they need to be permanent? There has been a tendency to use targeted permanent quadrats for monitoring bogs in the U.K. (e.g. Lindsay and Ross, 1994) despite the fact that the resulting data is not amenable to multivariate analysis.

4.6.2 Marking Monitoring Positions Whatever methods are chosen for vegetation monitoring, the monitoring position often needs marking. They can be marked in a variety of ways. Bamboo garden canes are generally suitable; they are inexpensive, light to carry, easy to install, easy to find, last for about four years and are easy to replace when necessary. However, on sites grazed by large herbivores such as sheep and deer or where vandalism is a realistic threat, canes can easily be broken or pulled out and more substantial markers, such as stakes, may be necessary. Buried metal markers can be used in addition to, or as an alternative to, stakes and canes. For precise location, a 1cm x 30cm steel rod can be pushed vertically into the peat or for less precise location, a polythene wrapped 10 x 10cm aluminium plate can be buried horizontally just below the surface. Buried metal markers can be relocated using a metal detector. Canes or posts marking the general location can be allied to buried metal markers which enable precise repositioning for future recording, for example, metal rods protruding at the two opposing corners of an area quadrat or at the ends of a point quadrat frame. Handheld GPS devices are now commonly used to record monitoring positions. Current devices have centimetre accuracy.

4.6.3 Using Quadrats

93


Conserving Bogs

4.6

Monitoring and Site Assessment

4.6.3.1 Introduction Vegetation quadrats are areas or space in which attributes of plants are recorded. Consideration must be given to the location or positioning of quadrats and of the type of quadrat and recording scale to be used. 4.6.3.2 Location/Positioning At the outset, the method for locating quadrats needs to be determined. Common positioning strategies are: random, stratified random, along a transect or on a grid. Whether to resurvey in the same or different locations must also be determined. These decisions relate primarily to the objectives of the monitoring programme (see 3.4.3.2) but also to the size and complexity of the study area and the time and personnel available. Random Quadrats: A random quadrat pattern is not affected by other features and is, theoretically, the most objective way to locate vegetation quadrats. However, quadrat site location can involve much trampling and relatively large numbers of quadrats may be required to adequately characterise a study area. It is recommended that random numbers are used to locate quadrat positions. Random number tables are found at the back of some statistics books or they can be generated by personal computers. Except when 'needs must' it is not recommended that the 'throw over the shoulder' approach is used. This can introduce a degree of selectivity as the practitioner has to decide where to stand before throwing. For speed and ease or if only one person is available, distances can be paced. A long measuring tape can be used if two people are available and if greater precision is required. Procedure:  Pace or measure the length and width of the study area.  Select random numbers.  Mark out a baseline along one side of a study area.  Pace or measure along baseline and place garden canes at positions identified using the random numbers.  If transects of quadrats are being located use these baseline positions as the start of the transects and pace or measure along transects marking quadrat positions using random numbers.  If a totally random scatter is being located, pace or measure a random distance at right angles to each of the baseline markers to locate one quadrat. Repeat until the required number of quadrats has been located. In this case, random numbers should be paired, one number along the baseline and one offset from the baseline.  Alternatively, a random 'zig-zag' can be walked across the study area and at intervals canes left to identify quadrat positions. Stratified Random Quadrats: Stratification implies some degree of pre-selection based on an existing knowledge of a study area, for example, knowledge of vegetation types, surface features, drainage pattern and so on. If, for example, it is decided to monitor the vegetation of hummocks and wet hollows or of intact and damaged areas, a stratified random approach may be suitable. Although slightly less objective than a totally random approach it does allow a degree of targeting of effort. Again much trampling can result from this method. It permits easier comparison of different features as equal numbers of quadrats are located in each "stratified" feature. Procedure:  Position a baseline along one side of the study area or along each of the stratified features as appropriate.  Pace or measure study area or features, select random numbers and randomly mark baseline as described above.  Using random numbers, pace or measure out from baseline positions until the required and equal numbers of quadrats have been located in each stratified feature or area. 94


Conserving Bogs

4.6

Monitoring and Site Assessment

 Or, if size and distribution of stratified features allow, quadrats can be located by the random 'zig-zag' method described above.  Or, if features are small or scattered, it may be appropriate to throw a cane to randomly select quadrat sites. Grids and Transects: A grid pattern is suitable for monitoring whole site changes or for relatively uniform study areas. The grid intersects determine quadrat locations. A grid is sometimes considered to give a better representation of vegetation than a totally random approach (Greig-Smith, 1952). Because quadrats are at regular intervals, grids may not be suitable for use where the study area has a regular or repeated pattern of surface features. Procedure:  Install reference markers at the ends of grid lines.  Hold a measuring tape between two reference markers and temporarily mark quadrat positions, at regular intervals along the tape, with canes. A grid is in effect a series of parallel transects; therefore, the same approach can be used to locate transect quadrats. Quadrats can be located along the transects at regular intervals or randomly. Targeted Quadrats: At times it may be necessary to target quadrat locations. For example, there may be too few examples of a particular feature for random selection to be carried out. Relocating Permanent Quadrats: The relocation of quadrats is an important consideration. In a random or stratified random design a completely new set of quadrats could be located for each recording period. However, detected change may just reflect the differences between quadrat positions each time the quadrats are monitored. Usually quadrats are marked in some way to facilitate their relocation (see 4.1.3.2). Siting canes or posts a fixed distance away from the quadrat minimises the risk of eutrophication from perching birds. Visible markers may not be necessary for grid or transect-based quadrats. Place visible markers at either end of grid lines or transects so that when recording quadrats, a tape can be laid out between the end markers and a cane placed at the quadrat position. Precise relocation can then be achieved with metal rods or even wooden pegs or canes raised only slightly above the ground surface over which the corners of a quadrat frame or against which the legs of a point quadrat frame are placed. 4.6.3.3 Quadrat Types There are three main types of quadrat: area, point and line. All are useful for monitoring purposes but area and point quadrats are the most widely used. The type of quadrat and its size and shape may depend on characteristics of the bog and on the objectives of the monitoring programme. Factors or questions to be considered are:  Vegetation community mosaic - is there one, and what size are the component vegetation types?  Should the mosaic be monitored as an entity or as a number of associated vegetation types?  Which data are most appropriate - percentage, cover-scale or other?  How much time is available for recording the vegetation?  Are inter-site comparisons to be made and if so will the techniques or data sets be comparable?  How much detail is required?

95


Conserving Bogs

4.6

Monitoring and Site Assessment

Figure 4.29 An area quadrat suitable for monitoring bog vegetation. The quadrat is only 45cm wide so that the whole quadrat can be examined without trampling the vegetation. The ladder further minimises trampling Area Quadrats: Area quadrats can vary in size and shape. They are mostly within the range of 10 x 10 cm to 10 x 10 m. The commonest size is 1 x 1 m but this is often considered too large for bog monitoring as recording would result in trampling damage along at least two sides of the quadrat. A small square or rectangular quadrat frame (Figure A.29) used singly or in pairs is recommended. Quadrat frames can be constructed from 2 cm plastic tubing joined by elbow connectors or from lengths of angle iron held together by wing-nuts. Whatever the chosen material, 3 or 4 mm holes should be drilled along each side at 5 or 10 cm intervals. Elasticated thread can be secured through the holes to subdivide the frame. Subdivisions of 10 x 10 cm are generally suitable. The abundance of each species or of selected key species is estimated visually. This can be done for the quadrat areas as a whole or for each individual subdivision separately. Estimations based on subdivisions are more accurate and mean and variance values can be computed. Species abundance (not to be confused with relative frequency) can be estimated as a cover percentage, a cover value or a frequency value. There are a number of cover abundance value scales. The ten point Domin scale (Table 4.5) is most widely used. Other scales based on four or five points occur are used but they may be too coarse to detect all but major vegetation changes although some workers find the narrow middle bands of the Domin scale difficult to apply. It may be just as useful to opt for gross changes as recorded by a five point scale, for example. It should be noted that the National Vegetation Classification (Rodwell 1991 et al.) uses the Domin scale. Table 4.5 Domin values and their equivalent cover percentage ranges. Domin Value

Cover (%)

1 2 3 4 5 6 7 8 9 10

<1 1-2 2-3 3 - 10 10 - 20 20 - 33 33 - 55 55 - 75 75 - 95 95 - 100

Species frequency can be calculated by recording the presence or absence of each species in each subdivision of a quadrat. This is not recommended as the cover or quantity of a species can change substantially without the frequency value changing, particularly if plants of a species are scattered rather than clumped. Also, species with the same frequency values may have hugely different percentage covers. Species with frequency values of 50, for example, may have cover values ranging from just a few percent to nearly 50 percent.

96


Conserving Bogs

4.6

Monitoring and Site Assessment

Mapping: An advantage of establishing permanent area quadrats is that the distribution and cover of plant species can be mapped sequentially with time. Sequential mapping gives a strong visual impression of vegetation change (e.g. Lindsay and Ross, 1993). Point Quadrats: When visual estimates of percentage cover and cover abundance values are not detailed enough, it may be necessary to monitor using point quadrats. Point quadrat work can, however, be very intensive and time consuming. This method is considered to be the most objective and quantitative means of estimating species composition and change, and it is particularly useful for monitoring vegetation changes associated with management changes (Grant, 1993). Point quadrats (Figure 4.30) are recorded using a frame which supports one or a row of regularly spaced, sharpened needles. The frame may incorporate a height scale. The needles are slowly pushed through the vegetation, one at a time, towards the ground and all contacts with the tip of the needle are recorded. To avoid errors use very sharp needles, only record contacts with the tip, and incline needles at 32.5 o to the horizontal (Warren Wilson 1959). As well as recording species, plant structures such as flowers, leaves and woody stems can be noted. Cover percentage and relative frequency calculations are generally based on a minimum contact number of 500. In peatlands this will require between 100 and 200 needles. Either each cover figure should be based on a set number of needles or recording should continue until a specified number of contacts is achieved. Percentage cover is based on the number of needles that contact a species and cover abundance is based on the total number of contacts made by a species. % cover = No. of needles contacted x 100 Total no. of needles Relative frequency = No. of contacts x 100 No. of needles For example, if 200 needles are used and of these 100 needles Figure 4.30 A point quadrat frame make 300 contacts with species A, then percentage cover is 50 constructed from plastic pipe with one % and relative frequency is 150 %. Point quadrats frames with height scales cost about £800 and pin in position. The ends of the frame are solid plastic and the legs are held £2000 for single pin and multi-pin frames respectively. with wing nuts.The pin is held by a rubber ring to prevent it from slipping. Line Quadrats: Line quadrats are particularly suitable for monitoring mosaics or for monitoring vegetation transects across bogs. A measuring tape is a convenient line quadrat marker. Within vegetation mosaics the line quadrat should be long enough to include the principle features of the mosaic. Line quadrats along a transect of a bog can be contiguous or at regular or random intervals. A line quadrat can be of any reasonable length although lengths of 5 or 10 metres should be useful. There are two main ways of recording plants along a line quadrat:  at regular (for example, 10 cm) or random points along the tape, record the species in contact with one edge of the tape; or  measure the distance along the tape of each species contact. Line and point quadrats can be combined. Hulme (1986) recorded quadrats using a 10m line with frames of pins (e.g. 10 pins x 10 frames) randomly or regularly placed along the line. As well as recording the overall species composition, he was able to measure the proportion of the vegetation mosaic occupied by particular vegetation types and physical features (such as, wet hollows and pools).

97


Conserving Bogs

4.6

Monitoring and Site Assessment

4.6.4 Data Storage and Processing Vegetation data can be stored on paper or on a computer spread sheet. Either medium can be used to process the data to express cover as percentage or relative frequency values. When cover values have been calculated for a number of quadrats or plots and for a number of years they can be analysed or processed further. Two main approaches can be employed, namely simple graphing of results and numerical computer analysis of results. 4.6.4.1 Graphic representation The response of vegetation to management, land use pressure, site reinstatement, and so on, can be determined by graphing the cover of the principle or more significant species. This is illustrated in Figure 4.31 which shows the response of bog vegetation and peat depth to upland grip blocking. 4.6.4.2 Numerical analysis Numerical analysis is carried out using computers. Computer packages such as Minitab, Genstat, VESPAN (University of Lancaster) and MVSP (Kovach Computing), Stata, SAS, SPSS, ARC, Mplus, R and MATLAB contain a range of statistical and ordination routines suitable for analysing and representing vegetation changes. Correlation, regression and variance analyses, and so on, can be useful interpretative tools as can ordination techniques such as principal component, principal coordinate and correspondence analyses. Decorana and Canoco and so on (for example, Ludwid & Reynolds 1988; Parker 1991; Bailey 1992; Kent & Coker, 1992).

Figure 4.31 Graph showing percentage of different plant species and peat depth at 15 different quadrats.

4.6.5. Proxy measurements 4.6.5.1 Vegetation as a proxy Monitoring and quantifying variables such as greenhouse gas flux and carbon storage potential requires specialist training, is time consuming, and expensive. A â&#x20AC;&#x153;proxieâ&#x20AC;? approach has been developed in order to generate data that can be used to approximate other peatland variables such as water table and gradients, carbon storage potential and greenhouse gas fluxes. A methodology is being developed that uses vegetation 98


Conserving Bogs

4.6

Monitoring and Site Assessment

type as an accurate proxie for greenhouse gas fluxes. Mean Water level is strongly correlated with GHG emissions and vegetation form can be used as an indicator for water level so therefore GHG emissions. Current research being undertaken on the relationship between vegetation type and greenhouse gas emission the vegetation form concept (Joosten 2009) will substantially increase the accuracy of the proxy. Vegetation is a good proxy for GHG emissions as;  Allows for fine scale mapping.  Is responsible for part of the GHG emission itself due to the quality of the organic matter it produces and by providing possible pathways for increased methane emissions.  Is controlled by the same factors that determine GHG emissions from peatlands such as acidity, nutrient availability.  Reflects longer term water level conditions and therefore provides an indication of relative time scale. (Cited form Bonnett et. al., 2010, adapted from Joosten and Cowberg, 2009). Table 4.6 – Vegetation types in Ostrovskoe and Vygonoshanskoe with associated flux measurements and their standard deviations and best estimates of GWP. Vegetation type Bare Peat

Calluna Eriophorum

CO2 7.0 (± 2.6) for active extraction sites. 7.4 (± 0.9) for abandoned extraction sites. 1. As moist bog heath 3.3 (±2.1) 1. 2.

Polytrichum Moist bog heath Very moist bog heath

CH4 0.4 (±0.6) for active extraction sites. 0.06 (±0.0) for abandoned extraction sites. 1.

GWP 7.5

0.3 (±0.1) 1.2.

12.5 3.5

As bare peat 12.6 (±4.0) 3. 9.0 3.

Negligible 3. 0.7 3.

7.5 12.5 10

Moderately wet Sphagnum hummocks

Neglected

0.7 (±0.2) 4.

0.5

Wet Sphagnum lawn Very wet Sphagnum hollows

Neglected Neglected

5.2 (±3.2) 3. 12.8 3.

5 12.5

1. 2. 3. 4.

Remarks

Litter accumulation counteracts C losses from degrading peat. Mosses lack roots. With the same water levels, emissions are higher than from bare peat because plant roots change water regime, improve aeration and add labile organic compounds in the form of recently dead roots and root exudates that stimulates the decomposition of more recalcitrant peat. CH4 emissions increase with higher water levels. CH4 emissions from wet bogs in boreal regions are much lower that the values cited here. Published measurements generally show uptake of CO2 from rewetted bog sites. Water bourne carbon export is generally larger before rewetting. The values presented have discarded potential C sequestration and assume zero CO2 flux at rewetted sites.

Maljanen et al (2010). Tuittila et al (1999). Drosler (2005). Bortoluzzi et al (2006).

4.6.5.2 Nanotopes as a proxy Nanotopes refer to the smallest structural component of a peat bog, for example, a hummock. Recording nanotope accurately can give a clear indication of gradient and relative rates of water movement. Of great value when interpreting the data is that each nanotope which form the components of the microtope is characteristic of a specific moisture content and therefore peat density at that measured point (Lindsay 99


Conserving Bogs

4.6

Monitoring and Site Assessment

2010). Simply, nanotope can be divided into three terrestrial and three aquatic microform types and they occupy a specific height zone relative to the mean water table. They are highly sensitive to changes in the water table so if the site is disturbed and there is water table draw down then terrestrial nanotopes will expand at the expense of the more aquatic nanotopes and vice versa. Nanotope monitoring can be integrated into a vegetation monitoring protocol and recorded in parallel on a site monitoring form. If recording nanotope form in parallel with individual quadrats they should ideally be representative of a single microtope zone. The location of the quadrat and nanotope form should be recorded using GPS if possible.

Table 4.7 Nanotope type, description and water table characteristics (Lindsay 2010) Nanotope type Description Water table characteristics Re-vegetation of any erosion gully or section of gully N/A E1 showing signs of revegetation. Revegetation Erosion gully actively eroding, so significant N/A E2 revegetation. Active erosion Evidence of impact on bog surface; burning, grazing, N/A Em1/2 trampling etc. Micro erosion Tk tussock T1 Low ridge T2 High ridge T3 Hummocks T4 erosion hags

Formerly eroded but undergoing significant vegetation recovery. Vertical range of 0-15cm. Highest prop of Sphagnum, richest zone for characteristic bog species. 15-25cm, characterised by bog and some heath species, Sphagnum cover variable. 25cm-1m. some bog species and several heathland species, notably heather. Supports several heathland spp, and 1 or 2 bog species, dwarf shrubs and lichens common. 0-10 cm, species poor, dominated by S. cuspidatum, perhaps stands of cotton grass.

N/A 0 – 15 cm above average water table 15-25 cm above average water table 25cm – 1m above average water table Vertical zone 0.75m – 1m+

A1 Sphagnum 0cm - -10cm below average water table hollows A2 Mud bottom Shallow pools no more that 20 cm deep, mud or Shallow pools no more than 20 cm deep decomposed vegetation for base. hollows For a full and detailed description of nanotopes and microtopes see last appendix of Richard Lindsay 2010 publication entitled “Peat Bogs and Carbon – a critical synthesis”). Patterns of nanotopes can give a very clear indication of gradient and relative rate of water movement. Additionally, each nanotope is characteristic of a particular moisture range and consequent peat density in the peat at that specific point (Lindsay 2010). It is possible to make accurate inferences regarding the status of the water table if nanotope form is accurately recorded. Table 4.8 shows methane emmisions and nanotope estimated by Laine et. al. (2007) from differing parts of blanket bog in Co. Kerry, Ireland (adapted from Peatbogs, a critical synthesis by Richard Lindsay 2010).

Nanotope

T3 Hummock T2 High Ridge T1 Low Ridge

Annual Daily CH4 emissions (mg CH4 m-2 CH4 yr-1) Median Water emissions Average Range level (cm) (g CH4 m-2 yr-1) 3.3

11.8

0.1-64.1

-13

5.8

19.2

0.0-72.2

-5

6.1

20.9

0.1-101.4

-1

100


Conserving Bogs

4.6

Monitoring and Site Assessment

Non vegetated A2 3.5 11.6 1.7-31.8 3 hollows Vegetated A2 13.0 50.4 0.3-263.0 5 hollows Table 4.8 Methane emissions and nanotope estimated by Laine et. al (2007) from blanket bog in Co. Derry. This table can be used to very broadly infer greenhouse gas emissions relating to nanotope forms, taking into account all the caveats associated with extrapolating data to different regions.

4.6.6 Remote sensing and image interpretation The science of environmental remote sensing covers all means of detection and measurement from a distance (including digital cameras). There are an increasing number of instruments that operate over both visible and non-visible wavelengths. Although the use of many of these instruments is highly specialised, it is important that the land manager is aware of their existence and their potential applications to mapping and monitoring problems. This section deals with general principles, common satellite remote sensing systems and some more specialised instruments, including thermal imagers. 4.6.6.1 Aerial Photograph Interpretation Aerial photograph interpretation (API) allied to ground survey is particularly useful for assessing vegetation variation across a whole site. The precision of API depends on the quality and resolution of the photograph. Remotely sensed images can be used to map vegetation. The basic idea is that each vegetation type has a unique signature in relation to how it reflects radiation at different wavelengths; its spectral signature. So, if you identify a known vegetation type on digital imagery and determine its reflecting properties, it is them possible to identify all the other areas of the image with the same properties. This process is called image classification (see 4.6.6.3). Commercially flown aerial imagery is available as standard Red Green Blue (RGB) photograph format. These are the most commonly used images for interpretation and are commercially available over large areas at a resolution of 25cm. Colour infrared (CIR) imagery determines wavelengths ranging from 700nm to 900nm at a standard resolution of 50cm. CIR imagery can be beneficial for interpreting peatlands using image classification for the following reasons; ď&#x201A;ˇ

CIR is widely used for soil mapping. The colour characteristics of soils are usually well defined and the homogenous nature of the peat signal generated from CIR images should improve mapping accuracy.

ď&#x201A;ˇ

CIR enables differences in soil moisture content to be determined; darker areas contain more water. Taking season and rainfall into account CIR photography could provide qualitative information on trends in peat moisture content in restored and unrestored areas.

ď&#x201A;ˇ

CIR photography is also useful for analysing water depth and sediment content. Clear water appears very dark and as sediment content increases the shades shift to a blue colour tone.

101


Conserving Bogs

4.6

ď&#x201A;ˇ

Monitoring and Site Assessment

Plants that are photosynthesising reflect a significant amount of infrared energy. As a result, healthy photosynthesising plant communities appear bright red on CIR photography. Areas that are covered with dead or dying vegetation show up as shades of white and grey. The NIR band is very effective at extracting spectral signatures for vegetation.

Figure 4.32 Red green blue aerial photograph (left) and colour infra-red photograph (right) of moorland in the Yorkshire Dales Ideally, multispectral and hyperspectral aerial imagery is be the best format to use for image classification but at present it isnâ&#x20AC;&#x2122;t widely commercially flown and available and can be costly. Multispectral remote sensing technologies, collect data from three to six spectral bands from the visible and near-infrared region of the electromagnetic spectrum. Over the past two decades, the development of airborne and satellite hyperspectral sensor technologies has overcome the limitations of multispectral sensors. Hyperspectral sensors collect several, narrow spectral bands from the visible, near infrared and short-wave infrared portions of the electromagnetic spectrum. These sensors typically collect 200 or more spectral bands, enabling the construction of an almost continuous spectral reflectance signature. Hyperspectral data at a finer spectral resolution can be used to improve vegetation classification, by detecting biochemical and structural differences in vegetation. Research is underway to determine if data of a higher spectral resolution could be used to discriminate vegetation at individual genus and species level (Govender et. al, 2008). On-line tools such as Google Earth and Bing maps are providing aerial images to a wider audience and can be used for limited interpretation if acquiring images proves too costly 4.6.6.2 Satellite Imagery One very important advantage of satellite-borne sensing systems over airborne ones is that they provide the opportunity for regular coverage of an area at relatively low cost. They are, therefore, potentially useful for monitoring purposes. The resolution and frequency of coverage is set by the satellite orbit. Polar orbiting satellites operate nearer to the earth, typically around 900 km, to provide higher resolution imagery. Geostationary satellites are positioned over the equator at altitudes of around 36,000 km, so as to progress at the same speed as the earth rotates - hence geostationary! The trade-off between these two orbital configurations is the frequency of imaging. Geostationary satellites can provide imagery on an hourly basis over very large areas of the earth. Polar orbiting satellites can cover the whole earth in 12 hours although only by using wide-angled viewing and thus trading off resolution for frequency of coverage. By increasing the resolution, using longer-focal length lenses, polar orbiting systems can provide resolutions of 10m but the time between overpasses is increased to 16-18 days. Most weather satellites are either geostationary or polar-orbiting with wide angled imaging systems (these produce the sorts of images you see on television weather bulletins). The typical pixel sizes are 4 km for the geostationary images (e.g. Meteosat) and around 1 km for the polar orbiting images (e.g. Tiros - N). 102


Conserving Bogs

4.6

Monitoring and Site Assessment

Although weather satellites provide daily image cover, the ground resolution of this imagery is so poor that it is unlikely to be of any practical value to the management of small areas of bog. There is some limited use to be made of this sort of imagery, for example, looking at time-series of vegetation development, over very extensive bog areas (e.g. northern Canada) but probably not in western Europe. It is the families of earth observing satellites which are likely to be of more interest to the bog manager. The principal ones are the US LANDSAT series and the French SPOT series. These are described below. The first LANDSAT was launched in 1972. Since then there has been regular imagery available for most of the earth, except high latitudes. All the satellites have multi-spectral scanning instruments. The existing instrumentation, the Thematic Mapper, gives image cover every 16 days with a pixel size of 30m - or just about one-quarter of the size of a football pitch! It also records in seven spectral bands, across the visible, near middle and into the thermal infrared. However, because the thermal band has a poorer ground resolution (c. 100m) and the imagery is taken in mid-morning (c. 09.30 local time), the quality of the thermal data is much poorer. Since the first Landsat satellite was launched in 1972, a series of more sophisticated multispectral imaging sensors, named TM—Thematic Mapper, have been added ranging from Landsats 4 (1982), 5 (1984), 6 (1993, launch failed) to 7 (1999) (Enhanced Thematic Mapper Plus, ETM+). The Landsat TM and ETM+ imaging sensors have archived millions of images with a nearly continuous record of global land surface data since its inception. Landsat provides medium to coarse spatial resolution images. For example, Landsat ETM+ imagery has a spatial resolution of 30 m for the multispectral bands and 60 m for the thermal infrared band (Xie et.al., 2008). To make it easy to get LANDSAT data, there is a standard Worldwide Reference System. In this, the orbit is called a path and the image is centred on a row. Each image covers an area 180 km x 180 km. So if you wanted imagery of North East Scotland you would order Path 205, Row 20. All UK images are obtainable through the National Remote Sensing Centre. They can be purchased on computer media or as film products (prints, negatives and so on). The French SPOT satellites were first launched in 1986. They carry a similar multi-spectral scanning system to LANDSAT although there are important differences. The first SPOT instruments operate in 2 modes. A black and white (panchromatic) mode which gives images with a pixel size of 10m, and a multispectral mode giving a pixel size of 20m. The scanner is also "steerable". These means that it is possible to get, by request, more frequent coverage. (This costs a lot!) It also allows the acquisition of overlapping imagery. So some SPOT imagery can be viewed in stereo. The coverage of a standard SPOT scene, however, is only 60km x 60km or less than one-quarter of the LANDSAT equivalent. Five SPOT satellites have been launched to date, from SPOT 1 to SPOT 5 in the year of 1986, 1990, 1993, 1998 and 2002, respectively. SPOT imagery now comes in a full range of resolutions from 1 km global scale (SPOT vegetation imagery) down to 2.5 m local scale. Two HRV (High Resolution Visible) imaging instruments on SPOT 1, 2 and 3 and the corresponding instruments of HRVIR (High Resolution Visible and Infrared) on SPOT 4 and HRG (High Resolution Geometry) on SPOT 5 scan in either panchromatic or multispectral modes. In addition, SPOT 4 and 5 also have a second imaging instrument referred to as SPOT vegetation (VGT) instrument that collects data at a spatial resolution of 1 km and a temporal resolution of 1 day. SPOT images, particularly SPOT VGT, are very useful for observing and analysing the evolution of land surfaces and understanding land changes over large areas (Xie et. al. 2008). Table 4.9 shows a summary of additional satellite imagery available. Satellites MODIS

AVHRR

Features

Vegetation mapping applications

Low spatial resolution (250–1000 m) and multispectral data from the Terra Satellite (2000 to present) and Aqua Satellite (2002 to present). Revisit interval is around 1–2 days. Suitable for vegetation mapping at a large scale. The swath is 2330 km 1-km GSD with multispectral data from the NOAA satellite series (1980 to present). The approximate scene size is 2400 3 6400 km

103

Mapping at global, continental or national scale. Suitable for mapping land cover types (i.e. urban area, classes of vegetation, water area, etc.). Global, continental or national scale mapping. Suitable for mapping land cover types (i.e. urban area, classes of vegetation, water area, etc.).


Conserving Bogs

4.6

IKONOS

QuickBird

ASTER

AVIRIS

Hyperion

Monitoring and Site Assessment

It collects high-resolution imagery at 1 m (panchromatic) and 4 m (multispectral bands, including red, green, blue and near infrared) resolution. The revisit rate is 3–5 days (off-nadir). The single scene is 11 3 11 km. High resolution (2.4–0.6 m) and panchromatic and multispectral imagery from a constellation of spacecraft. Single scene area is 16.5316.5 km. Revisit frequency is around 1–3.5 days depending on latitude. Medium spatial resolution (15–90 m) image with 14 spectral bands from the Terra Satellite (2000 to present). Visible to near-infrared bands have a spatial resolution of 15 m, 30 m for short wave infrared bands and 90 m for thermal infrared bands. Airborne sensor collecting images with 224 spectral bands from visible, near infrared to short wave infrared. Depending on the satellite platforms and latitude of data collected, the spatial resolution ranges from meters to dozens of meters and the swath ranges from several kilometers to dozens of kilometers. It collects hyperspectral image with 220 bands ranging from visible to short wave infrared. The spatial resolution is 30 m.Data available since 2003.

Local to regional scale vegetation mapping at species or community level or can be used to validate other classification result.

Local to regional scale vegetation mapping at species or community level or used to validate vegetation cover extracted from other images. Regional to national scale vegetation mapping at species or community level.

At local to regional scale usually capable of mapping vegetation at community level or species level. As images are carried out as one-time operations, data are not readily available as it is obtained on an ‘as needs’ basis. At regional scale capable of mapping vegetation at community level or species level.

Satellite imagery can be expensive. It is worth contacting your local university Geography Department before using such imagery. Some existing images may be available at lower cost. There are several uses for satellite imagery: 1) As a base map: A great advantage of satellite images is that, unlike aerial photographs, they are relatively free of distortions and do not have to be merged together to provide coverage of larger areas. It is possible to produce a properly scaled, true-colour photo-product, which can be used as a base map in the field. Bearing in mind the size of the pixels the most appropriate scale for enlargement is 1:50,000 although 1:25,000 is possible but usually highly "pixelated"; you can see the pixels. 2) For vegetation mapping: Satellite images have been and are routinely used for mapping vegetation. In general, their use in mapping involves the use of a computer and image processing software. Scaled photo-products can be used to map vegetation communities. This can be done on colour imagery (true or false-colour, which is similar to infrared aerial photography in that green vegetation appears red). Alternatively, it can be done on an image for each individual band. The best way to do this is using a gridded overlay and ticking each cell as to whether it is in the vegetation class or not. An interesting and useful output from this approach is that vegetation gradients are realistically represented on the final grid map. 3) Monitoring vegetation state: Healthy green vegetation absorbs strongly at red wavelengths and reflects strongly at infrared wavelengths. As vegetation grows and dies there are related changes in the way it reflects light. These changes can be exploited as a means of remotely measuring vegetation state (development stage, stress etc.). The most simple vegetation measure is to take a ratio of the infrared to red reflectance. A high value represents a healthy green cover, a low value represents dead or senescent vegetation. Ideally for this information to be of most use it should cover a whole growing season and preferably several seasons so that general trends can be established. Monitoring vegetation state using high resolution satellite imagery is difficult due to the cost of the multiple images and the unreliability of coverage due to cloud cover. A simpler, more controllable alternative is to use ground based radiometers which simply record light reflectance at red and infrared wavelengths. These instruments can be incorporated into a routine monitoring programmes and cost around £500-£600. There are well developed relationships between vegetation index and percentage ground cover; slightly poorer relationships with leaf area index and net primary productivity. There have been very few studies that have 104


Conserving Bogs

4.6

Monitoring and Site Assessment

used radiometers for monitoring semi-natural vegetation and they would still have to be considered as "experimental".

4.6.6.3 Image Classification Image classification, in a broad sense, is defined as the process of extracting differentiated classes or themes (for example, land use categories, vegetation species) from raw remotely sensed aerial and satellite data. (Xie et. al 2008). Image analysis and classification techniques using high resolution imagery are commonly used to classify, for example, vegetation variation and bare peat distribution across a restoration site. GIS software packages can be used to classify vegetation types based on spectral signatures (reflection of radiation at different wavelengths) of different vegetation. Combined with statistical tools using Ordinance survey layers, the accuracy of such analyses can be further refined. This enables the accurate generation of vegetation type data and other peatland variables over large areas of the peatland landscape. There are two common approaches to image classification, both are based on the principle that a land cover class can be described by a unique spectral reflectance. The simplest approach is called unsupervised classification where the computer is asked to determine a user defined number of clusters. Each cluster represents a land cover class or sub class. The mean digital value for each input band could be represented as a spectral reflectance profile. The cluster represents the spread of values around the mean for the land cover class. After the classification has been completed each class should be examined and assigned a name. It may also be necessary to merge a number of classes into a single category. The second approach is called supervised classification. The objective is to extend, or extrapolate information on land cover types for a known area of the image to the unknown areas of the whole image. The image analyst defines a number of training areas for each land cover category. The computer generates spectral signatures based on this information. Typically, a maximum likelihood descriptor is used to measure the spread of values around the mean of the class. Each pixel of the image is assigned as far as possible to one of the land cover groups, as defined by the signature. A

B

C

A

Figure 4.33 Aerial overview of an area of eroding peat (A), dataset produced from image classification (B) and final dataset mapping all areas of exposed peat (C). There are advantages and disadvantages to both approaches. An unsupervised approach is useful where no prior ground information exists; is not biased in defining classes; is relatively rapid to compute; and accounts for all cover types in an image. However the process of identifying and merging classes can be time consuming and the statistical description of the spread of values within the cluster is not as good as the maximum likelihood classifier. Conversely the supervised maximum likelihood approach is time consuming when identifying training areas; relatively slow to compute; and can only produce a class map for which there are training areas. There are many types of computer software available that can perform image classification, for example, ESRI ArcGIS. Otherwise, maps can be drawn by hand providing the basis for the management planâ&#x20AC;&#x2122;s site description (see 3.1). 4.6.6.4 Thermal Imaging 105


Conserving Bogs

4.7

Monitoring and Site Assessment

There are other types of non-photographic imaging system. These include thermal imaging systems. Thermal imaging is a very specialised technology. It depends upon new sensors which can measure subtle changes in the radiant temperature of objects. Thermal cameras have been developed by the military and are generally used by emergency services for search and rescue purposes. They have had very limited applications in environmental monitoring; these have mostly been to do with heat loss survey of buildings. However, they are very sensitive to variations in radiant temperature detecting to 0.2oC. In Canada, they have been used to detect upwelling groundwater which has a different thermal regime to surface water. It is conceivable that there are some very specialised applications of this technology to monitoring bogs. The costs of these systems, in the order of £10 - 20,000, would indicate that they are likely to be used for experimental, rather than operational purposes. More recently, thermal imaging data and LIDAR have been used in conjunction to extract spatial data describing near surface wetness and hydrological behaviour of drained blanket peatlands in Exmoor UK. The relative thermal emissivity (Ɛr) of the ground surface is mapped and used as a proxy for near-surface wetness. The results show how moorland drainage and land surface structure have an impact on airborne measurements of thermal emissivity. Such data could be used to describe the spatially distributed nature of near-surface water resources, to optimize catchment management schemes (Luscombe, et. al., 2014).

4.7. FAUNA 4.7.1 Introduction Many different types of fauna can be and are monitored on peat bogs. Rare species are often monitored to assess whether populations are stable or increasing. It would be too lengthy to include details of all types of faunal monitoring here, although some of the monitoring methods for birds and invertebrates are outlined. This is because these two groups often respond rapidly to management works and can be a useful guide to the success of management.

4.7.2 Birds 4.7.2.1 Introduction Bird populations can change rapidly as a consequence of conservation management. Removal of large areas of scrub woodland and the creation of open water has a particularly strong impact. This allows the success of management to be monitored via bird recording as a surrogate measure for habitat change. Other objectives of bird monitoring programmes are:  to provide baseline data for previously unrecorded sites;  to provide information on species that have particular conservation interest;  to complement interpretation of hydrological and botanical data;  to provide information to non-specialist audiences; and  to supplement national bird monitoring programmes. There are several standard techniques used in Britain and elsewhere that can be adopted for monitoring birds on peatlands. These are:  Breeding Bird Survey aimed at monitoring populations of widespread and abundant species in the UK (4.7.2.2).  Common Bird Census designed to estimate national bird population changes through monitoring of sample survey sites (4.7.2.3).  Point Counts where all birds are recorded at a designated number of locations (4.7.2.4). 106


Conserving Bogs

4.7

Monitoring and Site Assessment

ď&#x201A;ˇ Transect Counts for large areas of uniform habitat (4.7.2.5). Though each technique is designed for a specific purpose, they can be adapted to suit the requirements of individual sites. The point and transect count methods are most adaptable as the other methods have been designed within a national framework. As with any form of monitoring, it is important to clearly define the objectives of the scheme and assess all resource requirements (see 3.4.3.2). The following is a very brief description of the four methods mentioned. For more information consult Bird Census Techniques by Bibby, Burgess and Hill (1992) or contact the BTO or RSPB at: British Trust for RSPB Ornithology The Nunnery The Lodge Thetford Sandy Norfolk Bedfordshire IP24 2PU SG19 2DL www.bto.org www.rspb.org.uk

4.7.2.2 Breeding Bird Survey The Breeding Bird Survey (BBS) was designed and implemented by the British Trust for Ornithology (BTO) as a potential successor to the Common Bird Census (CBC). One kilometre grid squares are randomly chosen. Two transects are established, 1 km long and 500m apart. The habitats along the transects are described and coded (BTO methodology). Bird observations are recorded at two visits (all species) and divided according to distance from the transect: within 25m, 25-100m, greater than 100m and in-flight. An average visit takes approximately 1½hrs depending on the habitat. 4.7.2.3 Common Bird Census The Common Bird Census (CBC) was established by the BTO in 1962. Its principle aims were to measure the background variation in bird numbers and the extent of population changes due to pesticide use and habitat changes. A national picture is extrapolated from a series of sample sites (plots) which are recorded annually. Approximately 40,000 individual bird territories are mapped from 300 plots visited during March-July each year. A total of ten visits per year are made to the plot. On each visit all birds seen or heard are recorded on a 1:2,500 map. When all the visits are complete for the year, the information is transferred to a species map which, when analysed, shows the territories of individual birds. The result is a series of maps for each plot, species and season showing the number and position of each territory. These then form the basis for the extrapolated national picture. The fieldwork and mapping requires at least 60 hours of work which inevitably limits the number of plots visited. 4.7.2.4 Point Counts Point counts can be an efficient way of collecting species abundance data. They are particularly good in scrub habitats as they avoid excessive disturbance to the birds. It is not particularly well suited to large areas of open bog as birds are disturbed on open bog. Points are selected either systematically or randomly within the study area. They should be spaced far enough apart to avoid duplication of individuals. Counts should last between 5-10 minutes. On longer counts individuals may be recorded more than once. If a distance estimate is given for each record, a crude estimate of population density can be expressed. This method has no standard, national approach and could be readily adapted to suit individual needs and resource limitations. 4.7.2.5 Transect Counts Transect counts are particularly useful in covering large areas of open habitat. There is no standard methodology although there are a certain number of guidelines which should be adhered to. 107


Conserving Bogs

4.7

Monitoring and Site Assessment

Transect lengths are variable; they are dependent upon habitat (longer for open habitats), ease of access and time limitations. They should be spaced widely enough to minimise the risk of duplicating sightings. The recorder walks the length of the transect at a steady pace and maps or records all sightings. Supplementary information on behaviour, sex and so on can also be noted. A distance estimate (from perpendicular to the transect) is also noted. This method may be particularly suited to bogs as many species are flushed from cover as the recorder walks the transect route. 4.7.2.6 Counting leks Leks are communal display arenas where males of some bird species e.g. red grouse attend for much of the breeding season throughout the day (adapted from Bonnett et. al 2009). Lek counts should be carried out at dawn in a position that will not disturb the lek. Count the maximum number of males present an hour before and an hour after dawn. Additionally count the number of females and enter on a standardised form. After several site preparatory visits one visit should suffice. http://www.blackgrouse.info/research/monitoring.htm 4.7.2.7 Mist Netting Mist nets are usually fine-meshed nylon nests suspended between two poles to capture wild birds. Mist netting is a popular tool for monitoring bird species diversity, relative abundance, population size, age, weight and sex. However, it is very time consuming, training and a license are required so is not always suitable for a peatland environment.

4.7.3 Invertebrates 4.7.3.1 Introduction Monitoring invertebrates on a bog can be a time-consuming, methodologically difficult exercise which demands a great deal of expertise on behalf of the surveyor. Resources rarely allow for a detailed study. However, some invertebrate monitoring can be rewarding. Where site comparisons are being made, the methodology should be consistent between sites. Where possible, surveys should be designed so that they can be easily repeated as part of longer-term monitoring projects (Fry and Lonsdale, 1991). Another consideration is the range of habitats across the site. Surveys should be planned in a systematic manner to cover the main habitats on the site. This is important, as the greatest diversity of invertebrates are often found within marginal habitats (lagg fens, scrub and so on) which, though interesting, may not be representative of the whole site. As with any monitoring, it is important to set out the objectives of the scheme carefully (see 3.4.3.2). Where possible, invertebrate monitoring should be linked as closely as possible with botanical and hydrological monitoring programmes on a site. Climatic records are also of importance in interpreting invertebrate monitoring data (Shaw and Wheeler, 1995). 4.7.3.2 Survey Types and Methods Fry and Lonsdale (1991) identify five types of general invertebrate survey - all of which are applicable to bogs. 1. Inventory surveys where the aim is to find out what there is and if anything is of significance in terms of community size, community structure, species richness, species rarity and faunal assemblages and so on. 2. Site invertebrate comparisons. 3. Evaluating the effects of management practices where the aim is to discover whether a certain management procedure is of benefit or detriment to the invertebrate fauna. 4. Impact assessment which requires predictions about the effects of certain proposed activities on the invertebrate fauna. 5. Rare species surveys in which specialists assess the present status of certain rare species on one, or a series of sites.

108


Conserving Bogs

4.7

Monitoring and Site Assessment

Most surveys involve some combination of the above. This list is useful in deciding exactly why the survey is required and to establish primary objectives (see 3.4.3.2). Methods to achieve such surveys can be divided into trapping techniques and direct counting techniques. Trapping techniques include: malaise (4.7.3.3), pitfall (4.7.3.4), water (4.7.3.5), light (4.7.3.6) and suction trapping (4.7.3.7). Direct counting techniques include: transect walking, netting, hand searching, use of quadrats (4.7.3.8). Advantages and disadvantages are shown in Table 4.10.

4.7.3.3 Malaise Traps Malaise traps are designed to sample large numbers of flying insects, especially flies (Diptera) and wasps (Hymenoptera), without the need of a power source. The standard Malaise trap (Figure 4.34) looks rather like a ridge tent made of netting, without sides but with a central vertical partition. The insects fly into the central partition and then move upwards toward the light eventually reaching the apex of the trap where there is a plastic collecting bottle. Some type of killing agent (for example, Vapona) can be placed in the bottle. Figure 4.34 A Malaise trap (from Kirby 1992).

Malaise traps are relatively inexpensive and have the advantage that they do not require any power source and can, therefore, be taken anywhere. The fact that malaise traps catch large quantities of insects is both an advantage and a disadvantage. If the time and expertise is available to identify all the invertebrates sampled, then malaise traps become a very useful tool for examining populations and communities of winged Survey Method Trapping Malaise

Survey Type

Advantage

Disadvantage

Cost

ALL ALL, 2, 3

Water Light

ALL ALL

Suction

ALL, 1

Easily standardised. sampling.

Samples large numbers Kills large numbers. Standardisation difficult. Methodologically unsound. Kills samples. Kills samples. Standardisation difficult. Power source needed. Traps limited range of taxa. Samples large numbers. Time consuming. Expertise essential. Poor in wet conditions.

Cheap

Pitfall

Samples large numbers. No power source. Simple to use. Expertise not always required. No power source. Simple to use. No power source. Used at night. Traps sample alive.

Direct Counting Transect walking

2, 3, 4, 5

Simple. No expertise required.

V. cheap

Aquatic-netting Sweep-netting Quadrat counting Sieving

2, 5 2, 3, 4, 5 3, 4 1

Extraction funnels

ALL

Simple. Simple. Simple. Simple. Samples lesser known invertebrates. Samples lesser known invertebrates.

Pooters

1

Samples very limited range of taxa. Requires regular repetition. Standardisation difficult. Standardisation difficult. Can be inaccurate. Expertise required for ID of smaller taxa. Expertise required for ID of smaller taxa. Time consuming. No standardisation.

Hand-searching

1

No standardisation.

V. cheap

Comprehensive

Simple. Can sample species not caught in traps. Simple. Can sample species not caught in traps.

V. cheap V. cheap Expensive V. expensive

Cheap Cheap Cheap Cheap Moderate Cheap

Table 4.10 Survey methods: advantages and disadvantages (survey types 1-5 refer to the list in Fry and Lonsdale, 1991). invertebrates. Under most circumstances, this will not be the case and many of the invertebrates sampled will be discarded or remain in perpetual storage. In these cases, the trap should be used sparingly or alternative sampling techniques used. 109


Conserving Bogs

4.7

Monitoring and Site Assessment

It is not recommended that malaise traps are used on small sites, (a good example is a small lowland raised bog) as this could have a detrimental effect on local populations of invertebrates associated with, or adapted to, those sites. Similarly, malaise traps should not be used where an endangered species is known to occur. A few useful guidelines when using a malaise trap are:  Change the bottle at least every two days in the summer months as sampled invertebrates soon begin to decompose. If the site cannot be visited every two days, use alcohol to delay decomposition for approximately one week.  Where there is scrub or woodland on the bog, place the trap at 90o to the edge of a block of trees - this catches the invertebrates hawking along woodland edges.  Loosely place some vegetation or tissue paper in the collecting bottle along with the killing agent - this helps prevent antagonism between individuals and increases the surface area within the bottle.  Malaise traps consisting of a collecting head, a spare collecting bottle, six metal tent pegs, two jubilee clips for attaching the head to the main support post, six strong nylon cords as guy ropes and an instruction sheet cost about £70.00 (2014). 4.7.3.4 Pitfall Traps Pitfall trapping (Figure 4.35) is a relatively simple and useful technique for sampling certain groups of invertebrates, particularly errant species such as ground beetles (Carabidae), rove beetles (Staphylinidae) and spiders. Many authors (Greenslade, 1964 and Holopainen, 1990) have questioned the use of pitfall traps as a survey technique and discussed the relative attractiveness to invertebrates of the various solutions used in traps. It is argued that the ‘catch’ reflects invertebrate activity rather than abundance and some species are always under recorded. Despite these drawbacks, it remains a useful technique with the bonus on bogs that traps can be easily sunk into the peat. Figure 4.35 A pitfall trap. Set into the ground, these intercept ground dwelling insects, they are particularly useful for catching active predators. In a survey of the ground beetle fauna of Welsh peatland biotopes (Holmes et al., 1993), pitfall trapping was used as the primary method of sampling along with hand searching and water trapping (see 4.7.3.5). In that case, white plastic vending cups, 70 mm in diameter x 80 mm deep, with a preservative solution of 10% ethylene glycol, 10% formaldehyde plus detergent were used. The preservative was necessary because the traps were only checked once every two weeks and many insects decompose in a water/detergent mix over that time period. Each trapping station had a line of five traps, two metres apart. Any sort of cup or container can be used as a pitfall trap but it is useful to follow these guidelines:  All containers should be of standard size and colour and spaced evenly along a transect.  All should contain the same solution.  It is a good idea to have the trap the same colour as the ground or surrounding vegetation, as some insects may be repulsed or attracted by particularly bright or dark colours. In the summer months an uncovered, light coloured trap may act like a water trap (see 4.7.3.5) for numerous flying insects, particularly flies, rapidly filling up the container.

110


Conserving Bogs

4.7

Methods and techniques for Management

 Always mark the site of the traps well; they are surprisingly difficult to find again.  Use preservative in solution if the trap cannot be checked at least every two or three days. An anti-freeze can be used in the winter months.  Pitfall traps are useful in survey and monitoring in conjunction with management where, for example, there are different grazing regimes on an extent of bog with the same hydrological regime or to monitor the change in invertebrate fauna before and after re-wetting.

4.7.3.5 Water Traps Water traps (Figure 4.36) are designed primarily to attract flying invertebrates. They consist of some sort of bowl or tray (metal baking trays are good) painted a bright colour and filled with water, a drop of washing up liquid reduces the surface tension enabling capture. White and yellow traps attract the greatest number of individuals but other colours, particularly black, may attract different species. Water traps do not provide absolute population estimates nor do they attract the full range of flying invertebrates. They are, however, very cheap and simple to use and can be useful in determining which are the most common species on the wing at any one time. Figure 4.36 A water trap. Many insects will settle into a liquid-filled container. Bright yellow or white containers are the best. For water traps to be of use in a monitoring programme, it is advisable to set the traps regularly through the spring and summer months in order to include a range of weather conditions. Setting the trap only once or twice a year and then repeating this on the same date in subsequent years may give misleading results as the sample taken depends upon the weather on that particular day. The following guidelines are of use:  When painting trays, use enamel paints as these tend to be resistant to water.  Traps placed at different heights above ground level attract different insects - use a square board nailed onto cut off fence posts as a platform.  When making site comparisons, ensure the traps are placed in similar types and heights of vegetation and that the survey is carried out at the same time.  Empty the traps daily if possible. Check the weather forecast - remember that on hot days, water evaporates whilst in wet weather water overflows.  Store specimens in alcohol, for example, isopropanol. 4.7.3.6 Light Traps Light traps are designed to sample night flying insects, primarily moths, although many other groups of insects may also be attracted to the trap. The trap usually consists of a powerful lamp set at the centre of a shallow funnel which leads into a closed box into which the moths are drawn. Once inside the box, the moths cannot escape and usually settle in amongst open egg boxes which are used to give the insects a resting place. Light traps have the advantage of catching insects alive and unharmed and are, therefore, ideal for survey work. Light traps can be useful for monitoring changes in the population of night flying moths in conjunction with management practices. The following guidelines are of use:  Be sure to use the same trap in the same place when monitoring population change from year to year.

111


Conserving Bogs

4.7

Methods and techniques for Management

ď&#x201A;ˇ Always release the insects caught in the trap back to the same site. Scatter individuals over an area in and amongst undergrowth to prevent predation from birds.

Figure 4.37 A light trap can be used to collect night flying insects. Therer are a number of designs in common use, of varying power, size and portability. 4.7.3.7 Suction Traps Of the techniques for surveying air-borne invertebrates, suction traps are the most accurate. They have been developed, standardised and their efficiency measured so precisely that aerial populations of invertebrates can now be assessed with a greater level of accuracy than those in most other habitats. A basic suction trap consists of an electric fan that pulls air through a gauze cone. The insects are filtered out and collected in a tube or bottle beneath. Traps can be fitted with a segregating device which can be set to switch at a given time. The advantage is that information on the flight period of insects can also be obtained. Absolute population estimates and information on invertebrate community structure can be obtained using suction traps. The disadvantages are that they are relatively expensive and can generate large samples which require arduous sorting and identification. 4.7.3.8 Aerial attractant traps Aerial attractant traps are designed to attract flies into containers with bait to be either trapped within the containers or guided upwards into collecting bottles. In order to attract the widest variety of species a wide range of baits can be used, for example, fungi, dung (adapted from Bonnett et. al. 2009) 4.7.3.9 Emergence trapping Emerging flies such as biting midges (ceratopogonids) and some caddis and mayflies can be caught in floating mesh boxes buoyed up by polystyrene floats. The flies then need to be sprayed with dilute alcohol and grasped with tweezers, placing the trap in a large polythene bag increases the efficiency of the technique (adapted from Bonnett et. al. 2009) 4.7.3.10 Direct Counting There are a number of direct counting techniques to estimate populations of given taxa. Transect counting: More conspicuous invertebrate groups, for example dragonflies and butterflies, can be monitored using the simple technique of walking a defined transect at a steady pace and counting all the individuals encountered. Once chosen, the route should not be altered. Annual comparisons are dependent on continuity from year to year and an annual index is dependent on weekly/monthly continuity. Sweep netting: For less conspicuous invertebrates dwelling within vegetation, sweep-netting is a useful technique. The surveyor need not count the entire 'catch' from every sweep but can concentrate on counting a few key taxa. Sweep-netting, when standardised over a given transect, is a useful and inexpensive monitoring technique. The same criteria also applies to aquatic netting which is a useful technique for monitoring aquatic invertebrates in bog pools and deeper hollows. Hand searching: This is another method of direct counting which, although almost impossible to standardise, can be useful for finding those species which defy other trapping efforts. It is particularly useful for finding ground dwelling Heteropteran bugs and invertebrates within vegetation tussocks (Kirby, 1992). Quadrats: Counting the number of an invertebrate species within a fixed quadrat is also a useful method. The quadrat should be surrounded by a Perspex, or similar, shield before counting begins to prevent individuals from escaping. This method becomes more difficult when the vegetation is tall and/or dense but could, for example, be of use on ground where bare peat is revegetating. 112


Conserving Bogs

Methods and techniques for Management

PART 5 METHODS AND TECHNIQUES FOR MANAGEMENT Many sites have been damaged in varying ways (see Part 1). In Part 3 (see 3.3), types of the damage were related to possible methods and techniques which may ameliorate the effects of that damage. These methods and techniques are laid out in the following sections. Note that some of the methods are well tried and tested, do not require great expertise to undertake and, taking a ‘do it yourself’ (DIY) approach, can be achieved rather cheaply. In contrast, other methods require specialist input and are expensive.

5.1 HYDROLOGY 5.1.1 Introduction 5.1.2 Dams 5.1.2.1 5.1.2.2 5.1.2.3 5.1.2.4 5.1.2.5 5.1.2.6 5.1.2.7 5.1.2.8

Introduction Plank Dams Plywood Dams Plastic Sheet Dams Metal Sheet Dams Peat Dams Composite Dams Plastic Piling Dams

5.1.3 Sluices & Weirs 5.1.3.1 5.1.3.2 5.1.3.3 5.1.3.4

Introduction Angled Pipe Sluices Wooden Plank Sluice Sheet Sluices (Gates)

5.1.4 Bunds 5.1.4.1 5.1.4.2 5.1.4.3 5.1.4.4

Introduction Peat Bunds Plastic & Peat Bund Clay Bunds

5.1.5 Ditch filling 5.1.6 Pumping

5.2. REVEGETATING PEAT SURFACES 5.2.1 Introduction 5.2.2 Natural recolonisation 5.2.3 Transplanting 5.2.4 Seeds and Spores 5.2.5 Rafting

5.3 MANAGING SCRUB AND TREES 5.3.1 Introduction 5.3.2 Cutting and Felling 5.3.2.1 Hand pulling 5.3.2.2 Hand Sawing 5.3.2.3 Brush Cutter and Chainsaw Felling

5.3.3 Scrub Control without Herbicides 5.3.3.1 5.3.3.2 5.3.3.3 5.3.3.4

Introduction Ring Barking Cyclical Cutting Controlling Scrub by Flooding

5.3.4 Scrub Control with Herbicides 5.3.4.1 Introduction 5.3.4.2 Chemical Spraying

113


Conserving Bogs

Methods and techniques for Management

5.3.4.3 Chemical Application by Weedwiping 5.3.4.4 Painting Cut Stumps 5.3.4.5 Application of Herbicide to Standing Trees

5.3.5 Waste Disposal 5.3.5.1 5.3.5.2 5.3.5.3 5.3.5.4 5.3.5.5 5.3.5.6 5.3.2.7 5.5.5.8

Introduction. On-Site Disposal Burning Waste Chipping Waste Dragging Scrub Off-Site Removing Trees by Helicopter Removing Trees by Tractor and Winch Specialist Extraction Machinery

5.4 GRAZING 5.5 BURNING 5.6. ACCESS PROVISION 5.6.1 Introduction 5.6.2 Raised Boardwalks 5.6.2.1 Introduction 5.6.2.2 Materials 5.6.2.3 Construction

5.6.3 Floating Boardwalk 5.6.3.1 Introduction 5.6.3.2 Materials 5.6.3.3 Construction Principles

5.6.4 Temporary Paths 5.6.4.1 5.6.4.2 5.6.4.3 5.6.4.4 5.6.4.5

Introduction Brash Paths Plastic Mesh Inflatable Path Plastic Path

5.6.5 Permanent Footpaths 5.6.5.1 Introduction 5.6.5.2 Materials 5.6.5.3 Construction

5.6.6 Short, Temporary Boardwalks 5.6.7 Permanent Roads and Tracks 5.6.7.1 Introduction 5.6.7.2 Materials 5.6.7.3 Construction

5.6.8 Temporary Vehicle Tracks 5.6.9 Vehicles

114


Conserving Bogs

Methods and techniques for Management

5.1 5.1 HYDROLOGY 5.1.1 Introduction Most activities which damage bogs cause direct or indirect changes to hydrology (see 1.8-1.14 and A1). Consequently, work to raise and stabilise waterlevels, through the installation of dams (5.1.2), bunds (5.1.4) and sluices (5.1.3) along with ditch filling (5.1.5) and pumping (5.1.6), is one of the commonest forms of bog conservation management.

5.1.2 Dams 5.1.2.1 Introduction Blocking open ditches requires the insertion of a series of impermeable (or nearly so) barriers. Initially, barriers (dams) raise waterlevels within the ditch back to the surface (Figure 5.1). Water still requires an exit over the barrier, so most dams should include a spillway or weir within their design, although, remember that the purpose of a dam is to bring water-levels back to the surface so spillways should be shallow. With the waterlevel back to the surface, the next priority is to revegetate resulting open water to effectively fill in the ditch. The timescales involved are varied; dependent upon the prevailing ditch conditions and their suitability for Sphagnum growth. The intention should be that the ditch infills during the lifetime of the dam. There are many different dam designs appropriate to different ditches, the resources available to the manager and the overall site management objectives. In most cases, however, it is the size of the ditch that dictates techniques and materials adopted for damming. Table 5.1 gives guidelines to the most appropriate dam types for varying sizes of ditch. There is still great potential for experimentation to increase damming efficacy and reduce resource requirements. Resources also have a bearing on the technique selected. A small peat dam (see 5.1.2.6) is inexpensive if labour is in ready supply. Plywood dams (see 5.1.2.3) are less expensive than plastic coated corrugated steel (see 5.1.2.5) and both require similar labour resources. Large plastic dams (see 5.1.2.4) have several advantages over solid plank dams (see 5.1.2.2); generally they are less expensive and are quicker and easier to install. Both large peat dams (see 5.1.2.6) and large composite dams (see 5.1.2.7) require the use of plant machinery and an experienced operator as they are too big to construct by hand. Consideration should also be given for vehicle access and the damage to the bog surface caused during construction (see 5.6). Table 5.1 Damming Guidelines Width <1m

Depth <1m

<2m

1m

>2m

1m

>3m

>1.5m

Material Peat (by hand) Polyethylene sheet and peat Ply sheet Corrugated steel Peat (by machine) Ply sheet Plastic sheet (unsupported) Plastic piling Peat (by machine) Plastic sheet (supported) Solid plank Composite Plastic piling Peat (by machine) Plastic piling Composite

115

Section 5.1.2.6 5.1.2.6 5.1.2.3 5.1.2.5 5.1.2.6 5.1.2.3 5.1.2.4 5.1.2.8 5.1.2.6 5.1.2.4 5.1.2.2 5.1.2.7 5.1.2.8 5.1.2.6 5.1.2.8 5.1.2.7


Conserving Bogs

5.1

Methods and techniques for Management

When blocking ditches over 1.5m deep it is recommended that a suitably qualified engineer is consulted at the planning phase. Whatever material is used, it is important that dam spacing and positioning are planned correctly. Judging the correct spacing of dams is important to a schemeâ&#x20AC;&#x2122;s success. Given an ultimate aim to raise waterlevels to the surface, water, backed up behind a dam, should reach the next dam just below its spillway (Figure 5.2).

Figure 5.1 The main principles of dam installation. In Figure 5.2i the dams have been spaced too far apart. This has two consequences: ď&#x201A;ˇ The speed of water falling from the spillway is increased which may cause scouring of the ditch base immediately in front of the dam. As the main pressure point for any dam is the base, failure is likely to occur there.

116


Conserving Bogs

5.1

Methods and techniques for Management

 Away from the dam, the surface of the water is well below the bog surface and the management objective is not attained.

By inserting two more dams (C & D between dams A & B), the waterlevel is maintained nearer the bog surface along its entire length (Figure 5.2ii). As the waterlevel in front of each dam is higher, the speed of flow falling from the spillway is reduced and potential scouring is minimised. The most accurate method for determining dam spacing is by surveying the ditch gradient with a theodolite or optical level (see 4.2). A profile of the ditch can then be drawn up and the number of dams determined. Alternatively, dam positions can be marked directly in the field by a person holding a staff. The levelling device is set-up at the end of the ditch and readings taken at regular intervals. When the correct drop in slope (usually 10-20cm) is reached, the point is marked with a cane. Ditch gradients are rarely constant rising and falling over short distances. This means that readings should be taken at several intervals along the ditch. As a guideline, a reading should be taken at least every 15m (more if the ditch obviously undulates). If the intention is to expend considerable resources on a damming scheme, appropriate planning at this level is necessary. The cost of contracting a survey or hiring of equipment is justified if the dams are eventually located in the correct positions. This type of survey can also be used to estimate the number of dams required - enabling better costing and organisation. Only the approximate location for the dam can be determined through levelling. The exact position depends on local factors. As a guide, avoid:  Large vegetation tussocks when installing sheet dams: they are difficult to cut through with a spade.  Trees: their roots are difficult to cut through and may also provide a conduit for water seepage.  Small depressions or rises along the ditch profile: similarly be aware of the topography immediately adjacent to the proposed dam site and avoid obvious gullies exiting the ditch. 

Cracked, oxidised and eroded peat banks where possible. Water that backs up behind a dam may soon find its way through such cracks and pass around the barrier.

Figure 5.2 Incorrect (i) and correct (ii) spacing of dams along a ditch. 5.1.2.2 Plank Dams Introduction Solid wooden plank dams (sometimes referred to as palisade dams) have been used very successfully on many sites in the past. Properly located and carefully installed dams can be used to block drains of a considerable size (over 1m deep and 2m wide). The installation of these dams can be carried out using non specialist labour (under experienced supervision).

117


Conserving Bogs

5.1

Methods and techniques for Management

Practical Considerations  The construction of solid plank dams is labour intensive.  Until further investigations are conducted on the effects of using chemically treated timber on bogs, it is recommended that untreated hardwood is used. However, such untreated wood is prone to rotting especially at the air/water interface. The most common woods used are oak, elm and larch.  The volume of timber required can be considerable. Timber may have to be transported to remote areas of bog over difficult terrain. Transport methods should be considered with regard to costs, practicality and potential damage to the bog surface (see A3.6.5, A3.6.6 and 5.6).  Prevent large groups of people congregating around the construction site; the peat will quickly become ‘puddled’ and this may lead to eventual dam failure.

Construction Method  Step 1 Lay a solid board across the top of the ditch overlapping the bank on either side by at least 50cm. This can either be used as a stringer or as a platform to work from. At this stage it is best to temporarily secure the board in place with wooden stakes at either end.  Step 2 Hammer in (using a heavy rubber maul or steel mell) the centre board in the middle of the ditch, making sure that the board stays vertical at all times. The centre board only one is chamfered on both sides. The board should be hammered in until its top is just proud of the immediate bog surface (Figure 5.3).

If several dams are to be constructed, make a metal cap to fit over the ends of the planks to protect them during installation. 1. Step 3 Alternating installation on either side of the centre, hammer in the other boards. To the right (facing the dam) all boards should have a right chamfer and to the left a left chamfer. This means that when the plank is hammered in, it is pushed tightly against the adjoining plank. Be certain to extend the dam well into the sides of the ditch (Figure 5.5).

 Step 4 When all the vertical boards are in place the horizontal stringer can be firmly secured to each board with a heavy duty nut and bolt (Figure 5.7). Alternatively, a

Figure 5.3 The first step in constructing a plank dam. second stringer can be added to sandwich the vertical planks in place, reducing the need to secure each plank with a nut and bolt. Every third or fourth plank should be sufficient.  Step 5 If a spillway is required, knock the central two or three planks down by the appropriate level (3cm is usually sufficient) - this level should now correspond to the bog surface. If the water level has to be controlled, sluice boards can be added to the front of the spillway (see 5.1.3) Figure 5.4 A protective cap used to stop planks  Step 6 Immediately after construction, small gaps maybe splitting and cracking when they are hammered evident between planks. As the wood swells these into the peat. usually disappear but to speed up the process wet peat can be forced into the gaps. The dam is now complete (Figure 5.8)

118


Conserving Bogs

Methods and techniques for Management

5.1

Figure 5.5 Vertical planks should be inserted in sequence with the chamfer helping to force the planks together Figure 5.6 Old ditches often have parallel secondary cracks which also require blocking.

Figure 5.8 A completed and working timber dam in the Yorkshire Dales

5.1.2.3 Plywood Dams Introduction Exterior grade or marine plywood sheets have been Figure 5.7 The vertical planks can be extensively used (see 6.9) to block small surface ditches. secured with nuts and bolts to a single Inserted across the ditch they act as impermeable membranes or double stringer arrangement reducing surface run off rates and raising local water levels. They are quick and easy to install and require few specialist tools; they can prove very cost effective. 119


Conserving Bogs

5.1

Methods and techniques for Management

Practical Considerations  Potential problems of rotting arise at the air/water/peat interface (below the water or bog surface little rotting occurs in the anaerobic environment). The situation is exacerbated by waterlevels fluctuating, promoting increased weathering from continual wetting and drying (Figure 5.9). However, dams have been in place in the Border Mires, Northumberland since 1985 and, as yet (1996), show few signs of rotting. If the top of the board is damaged (during installation) the layers of plywood may open up and rot quicker (Figure 5.10)

Figure 5.10 Damaged boards can rot quicker.

Figure 5.9 A plyboard dam is prone to rotting at the air/water/peat interface. If the water level can be maintained at the bog surface and Sphagnum quickly recolonised, rotting is reduced (Stuart Brooks)

 Plywood sheets can be obtained from most timber merchants. The standard size is 2440 x 1220 x 12 mm (8' x 4' x ½"), but they can be cut to any size either by the retailer or in the field with a panel saw. Large sheets need greater strength - 24mm thickness.  Boards should be carried on site by two people.  As with any dams the correct spacing along the ditch line is critical. (see 5.1.1).  To protect the top of the dam during installation, a protective "C" bar should be used, in conjunction with a heavy rubber maul (Figure 5.11).

Installation  Step 1 Site dams correctly (see 5.1.2.1).  Step 2 Cut a starter slot with a spade across the ditch. If using a normal spade only push it down to the bend in the shaft to ensure that the gap is not too big otherwise, once the dam is in place, water may find its way through and potentially wash out the dam (Figure 5.12).

When storing large sheets on site prior to installation, lay them as flat as possible on a plastic sheet to help prevent warping.

 Step 3 With the slot created, the board is pushed firmly in and held as vertical as possible. Now place the "C" bar on top of the board and hammer it in using the rubber maul. If a large board is being installed, two "C" bars

Figure 5.11 Hammering in a ply sheet dam. Note, the C-bar and the use of the rubber maul (Stuart Brooks). 120


Conserving Bogs

Methods and techniques for Management

can be used, one at each end of the board requiring a person at each end to hammer. The board should be hammered in until it is just above the bog surface (by 2-3cm).

5.1

Traditional peat digging spades (straight shafted) are ideal for this job as they can create a thin deep slot. A deeper slot means less hammering in. Specialist too-smiths can make up a straight shafted spade (Figure 5.13).

Figure 5.12 Water can pass around the side of the dam if the slot is opened out.

Figure 5.13 A basic design for a straight shafted peat spade, ideal for installing plywood or plastic dams

Concentrate the hammering at the ends of the board in alternate sequence. The maximum force is then placed on a smaller area and the board will go in much quicker. 2.

Step 4 To allow excess water to pass over the dam rather than forcing its way around the sides (leading to erosion and dam failure), it is necessary to add a small spillway. Cut a "V" notch with a saw in the middle of the board. To be effective the spillway need only be approximately 6cm wide and 3cm deep. The bottom of the spillway should always be just below the surface of the bog.

5.1.2.4 Plastic Sheet Dams Introduction Plastic sheets, usually comprising of an ultra-violet stable polyethylene base, can be used in a similar way to impermeable sheet dams. In Germany, they have been used extensively and successfully for over a decade. Plastic sheets and piling (see 5.1.2.8) have also been used in the UK. Depending on the application, the advantages of plastic sheets are:  100% impermeable;  inert; ultra-violet stable - should not break down or leach out chemicals into the bog;  very sturdy - capable of being hammered/driven in;  light and therefore easy to transport;  available in large sizes and thickness and can be joined together;  long field life (100 yrs.+); and  made from recycled materials.

Practical Considerations  The costs of using plastic dams are higher than plywood but they are likely to last longer.

121


Conserving Bogs

5.1

Methods and techniques for Management

 A "C" bar (see 5.1.2.3) should always be used when driving in the sheets with a heavy rubber maul. As plastic sheets tend to be thin (approximately 6 mm) a tight fitting bar, with elongated sides (20cm) should be used to stop cracking along the top edge.  When installing larger sheets, it may be appropriate to fit a hardwood or plastic stringer (horizontal beam) across the sheet prior to installation.  The size of the sheets are limited by three factors: 1. Rigidity across an open ditch. Large unsupported sheets have the tendency to bow under pressure. This can be countered by incorporating structural supports (Figure 5.14). 2. Installation problems. Manual installation restricts the depth to the height that a person can safely hammer from (i.e. below shoulder height). 3. Large sheets are difficult to manoeuvre, especially in the wind.  Excavation of an open slot for installing the sheet should be avoided where necessary as this could lead to problems of water seeping around the sides of the dam. However, a large board (>2m high) is difficult to hammer in without a slot. Therefore, a very narrow slot should be cut with a specialist tool or a traditional straight shafted peat (Figure 5.15).

Figure 5.14 Large plastic sheets can be strengthened by incorporating a horizontal stringer Installation  Step 1 Site the dam correctly (see 5.1.2.1).  Step 2 When the exact position has been determined - lay the board across the ditch. If absolutely necessary, use a spade, or specialist tool (Figure 5.15), to cut a starter slot across the ditch. To avoid erosion problems, take care not to open up the slot by pushing the spade backwards and forwards (Figure 5.12).  Step 3 Push the sheet into the starter slot keeping it vertical. Place the protective "C" bar (Figure 5.11) on top of the plastic sheet. This prevents any damage to the top of the sheet during installation.

122


Conserving Bogs

Methods and techniques for Management

5.1 Try to minimise the gap between the “C” bar and the sheet to prevent any cracking along its top edge. If a gap does exist small branches or wooden blocks can be wedged in to secure it in place. Ideally the “C” bar should be specifically designed to fit the plastic sheet.

Figure 5.15 A plastic piling, Mickle Moss, South Cumbria (Simon Thomas).

 Step 4 Hammer the sheet slowly into the peat with a rubber maul. Work from side to side until the board is fully inserted into

On small dams (<1.5m x <1m) a team of 3-4 people per dam is ideal. This allows each member of the team to circulate jobs and prevents too much fatigue! the ditch. The top of the dam should be just proud of the bog surface. 

Step 5 - When the dam is in place, cut a very shallow spillway at the centre.

5.1.2.5 Metal Sheet Dams Introduction Corrugated metal sheet dams have proved very successful in blocking small surface ditches. Practical Considerations  The most commonly used type of metal sheet dam is made from double-sided plastic coated corrugated steel (Figure 5.16). It is essential to use an appropriate "C" bar when installing the dam.  It is difficult to obtain sheets in widths of over 1m. Sheets can be joined with pop rivets though this may cause leakage along the join. Sheets are best used in narrow ditches (<1m wide). Installation  Step 1 Site the dam correctly (see 5.1.2.1).  Step 2 Cut a starter slot with a spade.  Step 3 Push the sheet into the starter slot and keep it vertical. Place the "C" bar across the sheet and hammer it in with the rubber maul. The sheet should be knocked down until its top is just proud of the bog surface.  Step 4 To deter water forcing its way around the side of the dam and washing it out, a channel should be created in the centre of the dam. A jab from the spade or a heavy blow with the "C" bar should be enough to make a sufficient dent to act as a spillway.

If two sheets need to be joined together, sandwich a thin piece of rubber (such as roof sealing strips) between the two and rivet in place.

123


Conserving Bogs

5.1

Methods and techniques for Management

5.1.2.6 Peat Dams Introduction An obvious dam building material on bogs is peat, given its low permeability, ready availability and no cost. However, the use of peat to build dams has many limitations and several factors should be considered prior to its selection. Practical considerations  Highly humified peat (Von Post H6-H8) is of low permeability and is suitable for use as a dam material.(see 2.3, 4.5.5.1). Lower permeability peats (humification of Von Post H3 and below) are unsuitable for use in dams as are very well humified peats (>H8).  When peat has been dried and exposed to air, it loses its ability to retain water (see 2.6.2). This process is irreversible so highly oxidised peats should never be used for dam building.  The size of the dam determines the technique adopted. Peat Figure 15.16 Installing a plastic dam, dams constructed by hand should be limited to ditch sizes less Mickle Moss, South Cumbria (Simon than 1m wide (Table 5.1). All other peat dams should be Thomas) constructed using plant machinery.  Wet peat is heavy; it is impractical to carry it by hand over long distances and vehicle use can potentially cause damage to the surface (see 5.6). The best option, therefore, is to take peat from the immediate vicinity of the ditch or preferably from within the ditch itself.  When constructing dams with plant machinery, adequate planning must be given to the movement of the machine across the bog during and after rewetting. Following dam construction large areas can rapidly rewet to make conditions unsuitable for heavy machinery. This should also be considered when planning for future maintenance work.  Peat is not completely impermeable so in dry areas (continental Europe, eastern Britain), it is better to use an impermeable membrane rather than peat to ensure maximum water retention.  On steep gradients peat dams are not suitable: 1. It is difficult to incorporate an effective spillway within the design of a small peat dam. Plastic pipes will either block, or the peat around them will erode away. Without a spillway to control excess run-off, water eventually erodes away the top of the dam or finds a way around the sides. 2. If the peat for the dam comes from the area adjacent to the ditch, a string of excavation hollows could act as a secondary parallel drain (see Figure 5.17).

Construction - Small Peat Dams  Step 1 Site the dams correctly (see 5.1.2.1).  Step 2 Mark out the position of the dam by cutting away the turf (top 20cm) on either side of the ditch in the exact position of the proposed dam (Figure 5.18).  Step 3 Remove the peat from the sides and base of the ditch (indent up to 40cm) leaving a clean wet peat face. If removing peat from next to the ditch, create a shallow slope into the ditch to promote the recolonisation of Sphagnum (Figure 5.18).  Step 4 - The peat used for the construction of the dam should be taken from either the ditch, upstream of the dam, Figure 5.17 A string of excavation hollows can or adjacent to the ditch (avoiding dried out or act as a parallel drain, especially on a slope, a unconsolidated peat).

problem when blocking ditches on blanket bog 124


Conserving Bogs

Methods and techniques for Management

5.1 If excavating hollows adjacent to the ditch do not unintentionally create another drain by leaving holes in a line spaced closely together (Figure 5.17). ď&#x201A;ˇ Step 5 Fill in across the ditch with wet peat compacting all the time to reduce permeability of the peat. If possible use large blocks of peat cut with traditional hand tools instead of small amounts. If peat is handled too much it loses its structure becoming a sloppy soup and making it impossible to work into a solid dam. Build up the dam until it is above the bog surface by approximately 50cm. This allows for any settlement or shrinkage (Figure 5.19). ď&#x201A;ˇ Step 6 The original turfs should now be laid back on top of the newly constructed dam. This will help prevent erosion of the bare peat face at the top of the dam (see Figure 5.20).

There is not normally provision for a spillway within a peat dam. On shallow gradients this should not be a problem, as water will diffuse around or over the top of the dam without causing erosion. However, if gradients are steeper and flows are strong, erosion across the top or the sides of the dam may be a problem. In this instance it would be better to construct another type of dam that could incorporate a stillway.

Figure 5.18 Plan view and cross section of a small peat dam

125


Conserving Bogs

Methods and techniques for Management

5.1 Figure 5.19 A completed peat dam standing proud of the surface by about 30cm.

Figure 5.20 Examples of small peat dams constructed in the Yorkshire Dales. Construction - Large Peat Dams Ditches of considerable size can be effectively blocked if an appropriate peat-type is used in conjunction with a low ground pressure excavator. The reach of the excavator must be sufficient to work the ditch from one side only, as crossing the ditch may be hazardous or impractical.  Step 1 Site the dams correctly (see 5.1.2.1).  Step 2 The machine operator experienced at working on deep peat sites and is aware of the potential risks and the management objectives of the particular task.  Step 3 - Start by excavating the vegetation in turfs (top 20cm) from the area designated for the dam. The dimensions of the dam are determined partly by the properties of the peat (Table 5.2).

Table 5.2 Large peat dam dimensions (for a ditch 3m wide). H-value (4.5.5.1)

Dam length <½m deep

Dam length 1-1½m deep

Indent

Height

over surface

Low (H3H5) High (H6-H8)

2m

4m

1m

30cm

1-1½m

2-3m

1-1.5m

50cm

As ditch size increases, all dam dimensions should increase to counter increased pressure.  Step 4 Clean out any unconsolidated or oxidised peat within the ditch to leave a fresh peat face. Indent into the banks on either side by approximately 50cm to key the dam into the side (see Figure 5.21).

126


Conserving Bogs

5.1

Methods and techniques for Management

 Step 5 The peat used to build up the dam can either be excavated from the zone in front (upstream) of the proposed dam or from a borrow pit behind the working arc of the excavator. In both instances, the top turf should not be used but skimmed off and placed to one side. Also, all oxidised or unconsolidated peat should be avoided as it is not suitable for dam construction. If a borrow pit is excavated, it should be deep enough to hold water throughout the year to enable Sphagnum recolonisation.  Step 6 Excavate wet peat and place it against a fresh cut face within the drain, making sure that adequate compaction seals the two surfaces together. Continue to build up the dam, compacting with the back of the excavator bucket at regular intervals.

Do not overwork the peat, as this results in loss of structure and leads to dam failure.  Step 7 When the peat dam is approximately 50cm above the surface of the immediate bog, the original vegetation turfs should be placed back across the top of the dam. A dam left unsurfaced erodes and may fail.

5.1.2.7 Composite Dams Introduction A composite dam is made of two impermeable sheets infilled with peat. In this instance, the peat merely provides the structural support for the dam and so peat of any quality can be used. A composite dam can also be used as a bridge for either vehicle or pedestrian access over a drain (see Figures 5.23 and 5.24). Construction Procedure

Figure 5.21 Construction of a large peat dam with an excavator

 Step 1 If dams are to be constructed along the entire length of the drain, determine their location by levelling (see 5.1.2.1). Access dams should be placed where convenient and preferably where the ditch is narrow.

 Step 2 The impermeable barrier can be constructed from either plywood (5.1.2.3), plastic (5.1.2.4/5.1.2.8) or corrugated sheet metal (5.1.2.5) and the appropriate methods for installation should be followed in each instance. Start with the sheet nearest to the upstream side (Figure 5.23) as this stops water making construction easier. The sheet should be pushed in leaving 10cm above the surface

 Step 3 Install the second sheet about 50cm - 1m from the first. A bridge for vehicles should be wider than for people.  Step 4 Remove any unconsolidated peat or vegetation from the inside of the two sheets, to leave a fresh, wet peat face. Turves should be placed to one side to be used to vegetate the surface of the infilled section.  Step 5 Infill between the two sheets compacting the peat down as work progresses. It is not necessary to use well humified peat as the sheets act as an impermeable barrier.  Step 6 If the dam is to be used as a bridge for either pedestrian or vehicle access, a layer of geogrid or geotextile (see 5.6.5) should be laid above the overflow pipe which in this instance should be enclosed.  Step 7 With the overflow and matting in place, finish off with vegetated turves.

If the dam is not to be used as a regular bridge, a half pipe can be used as a spillway. If necessary, cover with a piece of board to prevent peat falling in and blocking it up. 127


Conserving Bogs

Methods and techniques for Management

5.1

Figure 5.22 A large peat dam constructed with excavators, Yorkshire Dales. Figure 5.23 Construction principles of a composite dam. To stop the boards splaying out whilst compacting infilling peat, insert four vertical stobs, one at each corner, in front of the boards. Added strength can be gained by fitting horizontal cross-members underneath terram matting affixed to both boards.

Figure 5.24. Large composite dam with plastic piling and peat, Foulshaw Moss SAC (Simon Thomas). 5.1.2.8 Plastic Piling Dams. Introduction Pre-formed recycled plastic piling takes its design from metal piling used in the construction industry. So far, its use to block drains on peat bogs has been limited to just a few sites and, therefore, the technique is experimental. Results so far have been favourable and it appears that the material has considerable advantages over standard peat dams (5.1.2.6) and plank dams (5.1.2.2). The material is light (making transport easier), durable (at least 150 year life expectancy) and easy to work with (dams can be constructed very quickly). 128


Conserving Bogs

5.1

Methods and techniques for Management

Practical considerations. There are two types of plastic piling in the UK. The main differences concern the joining mechanisms and the final configurations (Figure 5.25). Choosing between the two systems depends upon individual requirements and personal preference.

Figure 5.25 Joint mechanism for two types of plastic piling. Both materials provide a reasonably watertight seal if the dam is constructed correctly. Installation procedure ( to 5m wide) The piling sections should be driven into the ditch, starting at the centre, and working progressively outwards. They can either be driven in with the hydraulic arm of an excavator or manually installed with a heavy rubber maul. Sections can be cut or ordered to any length (max. 8m). ď&#x201A;ˇ Step 1 Insert the central pile first. The central piles will usually be the longest and, if installing by hand, the most difficult. Piling with lengths greater than 3m cannot be easily or safely installed by hand.

Place a solid plank across the ditch and use this to work from. This makes installation easier and safer (by reducing the distances one has to stretch). To keep the piles in a straight line, run a taut line across the ditch and use as a guide. ď&#x201A;ˇ Step 2 The join acts as a guide for the next section. It should be possible to push the section the first 30cm into the unconsolidated peat. It is important to keep the piling as vertical as possible at the start.

To increase the effectiveness of the seal, flex each section against the next whilst hammering in. This should produce a watertight seal when the water backs up behind the dam. It is important to flex the sections in the direction of flow (Figure 5.17).

ď&#x201A;ˇ Step 3 - Work progressively towards the banks (Figure 5.27). Sections may be trimmed with a panel saw.

The dam may initially leak through the joins. These soon seal as peat particles plug the gaps. To aid this process a few handfuls of unconsolidated peat can be tossed into the upstream side of the dam.

129


Conserving Bogs

Methods and techniques for Management

5.1

Figure 5.26 Flexing the dam during installation in the direction of flow increases the strength of the seal.

 Step 4 When the correct height of the dam is reached, i.e. level with the surface of the bog, knock down the central pile about 3cm to form a spillway (Figure 5.28). Note that, the design of the dam requires a fairly high water pressure to help seal the joins by ‘bowing’ so a top stringer should not be added.

Figure 5.27 Plastic piling dams are best constructed in the following sequence, starting from the centre and working outwards towards the sides of the ditch.

130


Conserving Bogs

5.1

Methods and techniques for Management

A second configuration of the Plastic Piling Ltd sections is possible by inverting every other pile. This will form a "box" section, as opposed to the standard "deep-V" (Figure 5.29). The box section is technically a stronger design but forms a weaker seal (due to opposing forces) and is also more expensive (more sections are required per metre).

Figure 5.28 A completed plastic piling dam (Jason Smalley) Installation procedure (over 5m wide) To impound large volumes of water it may be necessary to construct the dam in a "box" sectioned format (Figure 5.29). However, from the experiences gained with smaller dams in box section it appears that opposing forces on the seals opens the joins and the dam leaks. In this instance a "hydro-seal" or an expanding polymer can be inserted into the gap (contact suppliers for advice). With the hydro-seal added, horizontal strength can be gained through the addition of backing stringers. These can be made from hardwood, or recycled plastic and bolted onto the back of the dam across its top edge (see Figure 5.30).

Figure 5.29 Plastic piling dams can be constructed in two configurations; the deep V minimises costs and is usually adequate for most situations but where the ditch is very large the dam may be best constructed in box configuration.

131


Conserving Bogs

Methods and techniques for Management

5.1

Figure 5.30 A long plastic piling dam constructed in box configuration can be strengthened using stringers and made watertight by inserting sealant or hydroseal into the gaps.

5.1.3. Sluices & Weirs 5.1.3.1 Introduction Sluices are channels or pipes used to regulate the flow or level of water and can be used to measure flow (see 4.3.4). They can either be part of a larger structure, such as an angled pipe within a bund (see 5.1.3.2, 5.1.4) or they can act as dams in their own right (see 5.1.3.3, 5.1.3.4). Waterlevel management is essential in many bog conservation schemes (see 2.5). Cutover bogs, in particular, require careful management as natural hydrological processes have been considerably modified. Inundation of fields connected by sluices is a common form of cutover bog restoration. Waterlevels on any bog are governed by the level of input from precipitation (see 2.5.1). In periods of high rainfall, surface run-off increases as the acrotelm saturates. Excess run-off may, therefore, need controlling to alleviate flooding of neighbouring land from arterial drainage systems. If a weir is used, discharge can be measured (see 4.3.4). Measuring water discharge past a specific point has several advantages: ď&#x201A;ˇ Discharge data can be used as evidence to counter claims of flooding by neighbouring land owners/occupiers. ď&#x201A;ˇ Data can be used as part of a more extensive hydrological monitoring scheme; especially pertinent to runoff/discharge/storage calculations (see 4.3.4). ď&#x201A;ˇ Discharge data can also be used as an indicator of management success or failure.

132


Conserving Bogs

5.1

Methods and techniques for Management

5.1.3.2 Angled Pipe Sluices An angled pipe sluice (Figure 5.31) is a hollow pipe with one or both ends attached to a swivelling right angled join. This allows the level of two water bodies, separated by an embankment, to be controlled. This type of sluice is extensively used on large rehabilitation projects where waterlevel control within enclosed waterbodies is desired. In most situations, an angled pipe sluice is incorporated into a peat bund or embankment (see 5.1.4). Practical Considerations  The diameter of the pipe should be large enough to cope with storm events. Guidance for pipe dimensions can be found in Featherstone and Nalluri (1988).  Vandalism is a threat in many locations. It is difficult to build into such a simple design vandal proof measures. Housing the assembly within a lockable enclosure can be difficult and expensive. If a threat does exist, an alternative sluice design maybe required (see 5.1.3.3, 5.1.3.4).  The pipe must be made from a suitable material capable of withstanding exposure and a regime of wetting and drying. Ultra-violet stable plastic pipes are the most suitable, these are available from local Figure 5.31 An angled pipe sluice and its use in an agricultural suppliers or specialist pipe stockists. embankment to control waterlevels in two separate water bodies. Installation  Step 1 - The sluice may either be incorporated into an already existing structure (e.g. a raised baulk between old peat fields) or into a newly constructed bund or embankment. When inserting the sluice into an existing baulk or bund, levelling should precede any work. The sluice should be placed at the lowest point of the bank and have the capacity to raise water to the optimum level required. Often, more than one sluice may be required. A stage board (commercial or home-made) can be located at the ends of the pipe. This allows greater precision when setting water levels.  Step 2 - Pipes should be buried at least 35cm below the surface to protect against trampling. Peat should be packed around the pipe to prevent seepage.

Collars attached to the pipe help prevent movement of the pipe within the peat and deter water from channelling around the outside. These can either be bought commercially or made from plastic sheeting.  Step 3 - With the pipe inserted, peat should be laid back over and compacted. Re-lay the peat with vegetation turfs to help prevent erosion of bare peat.  Step 4 - The swivelling right angled end(s) can now be set to the desired height (Figure 5.32). 133


Conserving Bogs

5.1

Methods and techniques for Management

5.1.3.3 Wooden Plank Sluice Introduction This commonly used design consists of hardwood planks fitted into metal or concrete channels which are keyed into the banks and base of the ditch. The height of the water is controlled by adding or subtracting boards. Practical Considerations  Unless a locking device is fitted, or the boards are set away from the bank, they can be easily lifted out and are prone to vandalism.  Unless properly machined, or fitted as a double layer, most plank sluices leak.  A firm foundation is important. Wet peat is not always stable enough to hold pressure built up behind the sluice and dry peat leaks and causes the sluice to fail.  Standard plank dams (see 5.1.2.2) can be readily modified to make a sluice (Figure 5.33) or the sluice can be constructed between concrete pillars and foundations.

Sluice Adaptation of Plank Dam Plank dams can be modified by adding steel (preferably) runners set into the upstream side of the planks to act as a guide for the horizontal planks. Wooden guides could be used but are less durable. A locking device can be added to the sluice boards to deter tampering. Figure 5.32 Plank dams can be modified to incorporate an adjustable sluice at the spillway to give a greater degree of water level control Specialist Plank Sluices Ready-made sluices are available as whole units that slot into place. The body of the sluice is constructed from glass-fibre reinforced concrete. This material is light, durable and virtually vandal proof. The design of the body includes a splashpan and moveable side rails. Boards are slotted into grooves in the side rails and bolted down with a locking bracket (Figure 5.33). It may be necessary to extend the sides of the sluice so it is keyed further into the peat banks. This helps to prevent seepage and erosion around the sides of the sluice.

134


Conserving Bogs

5.1

Methods and techniques for Management

5.1.3.4 Sheet Sluices (Gates) Sheet sluices have a limited application on peatland sites but can be adapted to allow variable levels to be set (Figure 5.35). The design incorporates double gates. At the base to allow complete drainage, and at the top used to set a variable water-level.

Figure 5.33 Plank sluices can be purchased ready made from BCM contracts Ltd. They are constructed from glass reinforced concrete and have horizontal wooden planks which can be added or taken away to set the desired water level. 5.1.4 Bunds

5.1.4.1 Introduction Figure 5.34 A design for double gate sluice. A bund is an impermeable embankment or barrier. It may be used to restrict water-losses or to impound open water. Materials used include peat (see 5.1.4.2), peat and plastic (see 5.1.4.3) or impermeable mineral materials - often clay (see 5.1.4.4). There are two types of bund. The first is raised above the peat surface to impound water (Figure 5.35). The second reduces lateral seepage with an impermeable barrier (Figure 5.36), e.g. at the margin of a bog or adjacent to active peat workings. The volume of water impounded by a bund is a product of the depth of water impounded and its area. This volume is also affected by the amount of incoming water, the efficacy of the bund and the permeability of the peat itself. In the UK, impoundment of large volumes of water (>25,000 m3 above the natural level of adjoining land) is regulated under the 1975 Reservoirs Act, it requires planning permission and must be planned under the guidance and supervision of a qualified civil engineer. It is also recommended that advice should be sought for smaller scale operations, particularly where adjoining land is outside the conservation area. Where water is impounded behind a structure, particular consideration should be given to the following: ď&#x201A;ˇ the resilience of the structure to wetting and/or drying; ď&#x201A;ˇ the likely high pressure and failure points (Figure 5.37); Figure 5.35 Raised bund designed to inundate the surface of the bog. 135


Conserving Bogs

Methods and techniques for Management

5.1

 the maintenance requirements and subsequent access provision for future management and;  provision for control of levels during particularly wet or dry periods (see 5.1.6, 5.1.3)

Figure 5.36 Internal bund designed to seal off subsurface flow at the bog margin.

For small bunds, internal baulks and sub-surface impermeable barriers, the risk of flooding adjacent landownings is small. Internal bunds are often obscured by water and peat so weaknesses are difficult to detect. However, every effort should be made to monitor the condition of the bund to detect any defects before they result in largescale failure. Whilst peat for bund construction may have to be brought in, it is best to use a local source due to transportation problems:  it may be costly if contract hauliers are required;  overhandling wet peat causes it to lose its structure, turning it into a runny soupy mess;  access to the bund site may be difficult if little infrastructure exists; and  it may be difficult to find an alternative site.

Figure 5.37 Likely stresses and failure points on a typical raised peat bund. 5.1.4.2 Peat Bunds Introduction Peat bunding is widely practised in the Netherlands and Germany. On cut-over sites, where both the acrotelm and catotelm have been destroyed, peat bunding has proved useful for re-wetting. Its use has now been extended onto more intact sites both on the periphery of the bog and on raised bog domes themselves. Not all peat is suitable for bund construction. Well humified black peat (H 6 - 8, see 4.5.5.1) is more appropriate for peripheral bunds. Less humified white peats may be utilised on internal bunding or reinforced with an impermeable membrane (see 5.1.4.3). Fen peats are variable in composition and should be examined carefully before deciding on their suitability for bund construction. Peripheral Bunding Peripheral bunds are constructed to minimise water loss via drainage and seepage at the edge of the bog, and to counter drying of the dome due to cracking and slumping at unnatural edges (Figure 5.39). The peat used for bund construction should ideally come from close-by. Extraction of peat could have archaeological implications (see 1.6, 3.2). It is suggested that an archaeologist is consulted prior to the start of work. The bund foundation may either be on mineral soils or on well humified peat (ideally of similar properties to the construction material). If the bund is built over weakly humified peat it may sink and, therefore, must be built to a higher level than is ultimately required (see 4.5.5.1). There must be a good seal between the bund and the peat face/foundation. To achieve this the outer 30cm (approximately) of peat should be stripped away to leave a fresh peat face and foundation. 136


Conserving Bogs

Methods and techniques for Management

If the peat used in construction is derived on-site, it should be excavated from the zone in front (bog-side) of the bund. The borrow pit may act as a reservoir for water storage and help maintain moisture levels within the peat bund (Rowell, 1988) preventing shrinkage and cracking. In an effort to deter erosion from waveaction against the bund face, the borrow pit should not directly abut the bund face, but should be inset to leave a wave 'shelf'. This platform may also provide a convenient working location for the excavator. (Figure 5.39) and act as a platform for rafting (see 5.2.5) vegetation (Wheeler and Shaw, 1995).

5.1

As the bund is built up, peat should be well compacted Figure 5.38 An unnatural edge (ii) causes cracking but not 'overworked'. The gradients of the bund edges and shrinkage in contrast to an undisturbed edge are determined by the properties of the peat but as a (i) which generally has shallower gradients and a guideline, 30-40 covers most situations. Where lagg fen. slopes are too steep, the bund may be prone to slumping as moisture content changes through wetting and drying; with shallow gradients, a larger volume of material is required to attain the same height. Streefkerk and Zandstra (1994) offer guidelines for bund dimensions based on experimentation at the Bargerveen (Table 5.3).

Figure 5.39 Bund construction showing the layout of the platform and borrow pit. Table 5.3 Bund dimensions. Water depth at inner side of bund (m)

Height of bund (m)

Width at top of bund (m)

0.50 – 0.75 0.75 – 1.00 1.00 – 1.50

1.50 2.00 2.50

3.00 4.00 5.00

Bunds be constructed allow forofshrinkage if the peat is poorly humified or It may should be necessary to extendtothe sides the sluiceand so itsettlement is keyed further into the peat banks. This very (80% + moisture content). helpswet to prevent seepage and erosion around the sides of the sluice. To stop over-topping and erosion of the bund, provision for outflows should be made at convenient locations. Overflow levels can be altered by using adjustable 90 angle pipes on the inner face of the bund (see 5.1.3.2). Peat sods (containing vegetation) or poorly humified peat should be layered over the finished construction to stimulate vegetation colonisation and deter erosion of the bare peat surface. Scrub should be prevented from establishing on bunds as it promotes drying and cracking. 137


Conserving Bogs

5.1

Methods and techniques for Management

There are a number of potential problems which should be assessed at the planning stage:  It is extremely important to determine accurately the correct height of the bund overflows to prevent inundation of areas of high conservation significance. Large bodies of open deep water is not be conducive to Sphagnum re-colonisation (Wheeler and Shaw, 1995) and attracts wild fowl and gulls which, through eutrophication, alters the chemical characteristics of impounded water.  Large areas of impounded water may pose a flooding risk to surrounding land. Manipulation of bog hydrology for conservation purposes may also affect areas which receive drainage, or runoff, from the bog. Landowners may be concerned about the possibility of flooding adjacent fields.  The re-wetting of the peat inside the bund may cause the bog to rise (if shrinkage had previously occurred), potentially altering gradients and water flow characteristics at or near the periphery (see 4.5.3, 4.3.3.6).  A long-term commitment to maintenance of the bund must be established (see 4.1). Following re-wetting, access to the inner face of the bund may no longer be possible; suitable alternative strategies must, therefore, be devised to maintain the bund (such as the provision of a sluice to completely drain the site should the need arise). Internal Bunding Internal bunding can increase water-levels on over-steepened increased gradients (following extraction, drainage and/or slumping) or to truncate dense drainage networks (see Figure 5.40). Figure 5.40 Internal bunding designed to (a) increase water levels on oversteepened gradients or (b) truncated drainage networks. To avoid damage during transportation, it is use a local peat supply. If local peat is inappropriate, provision should be made for temporary vehicle access (see 5.6.8). A low-ground-pressure excavator or an excavator working on bog mats is the most cost effective machinery for bund construction. When creating open water, the bund must protrude above the surface and be constructed from well-humified peat or contain an impermeable insert. In this situation, the same principles for peripheral bunding apply (Figure 5.41). Seepage through the top layers of weakly humified peat can be retarded if an internal bund of well humified peat is installed (see Figure 5.42).

5.1.4.3 Plastic & Peat Bund A bund may require the insertion of a plastic membrane to decrease its permeability if only low humification peat is available (<H5 - see 4.5.5.1). For this, non-toxic and non-biodegradable plastic or heavy duty polythene sheeting (available from builders merchants) can be buried within the bund. At Raheenmore internal bunding has been applied to a more or less intact peat dome. Streefkerk and Zandstra (1994) give the following guidelines:  An assessment of peat depths and properties should precede any construction (see 4.5.2, 4.5.5). Bunds should not be constructed over unconsolidated Sphagnum cuspidatum layers. 138


Conserving Bogs

5.1

Methods and techniques for Management

 A plastic membrane is inserted vertically into the bog surface within a narrow slot. It is not necessary to insert the membrane to the bottom of the peat body (Wheeler and Shaw, 1995) but it should penetrate to at least 1m. The plastic should be held in place as the slot closes against the sheet. Remember to leave a folded section of sheet to cope with the bog expanding as it re-wets.

Figure 5.41 Basic design for the construction of an internal bund designed to impound water above the surface level.  The top sod (vegetation layer) should be removed from the bog surface over the width of the bund base. This creates a good seal between the bund and the bog. To help stabilise the plastic screen, a small section of vegetated sod should be left on either side of the screen.  For long bunds (>20m), wooden posts should be hammered down to firm peat at the outside edge of the plastic screen. Posts should be spaced at every 5-10m to protrude above the bog surface by the desired water-level height. A notch cut into the top of the pole is used to attach a plank to the top of the plastic screen. As the bog swells, following re-wetting, the plastic screen can fold out.  Peat can be excavated from a borrow-pit 1-2m in front (bog-side) of the bund location (place the top sods to one side). The bund is built up around the plastic sheet and the wooden posts. It should be built to at least 50cm above the desired water level (top of the wooden posts) and eventually dressed with the top sods taken from the base and borrow-pit.  At regular intervals provision should be made for overflows. The easiest method is to incorporate plastic drainage pipes just above the horizontal planks.

139


Conserving Bogs

Methods and techniques for Management

5.1

Figure 5.42 Internal bund construction using highly humified (adapted from Wheeler and Shaw 1995).

Figure 5.43 Construction of plastic and peat bund (after Streefkerk and Zandstra 1994).

5.1.4.4 Clay Bunds The use of clay as a bunding material on nutrient-poor bogs is generally not recommended for the following reasons:  Drying causes clay to crack and leak. Excessive leakage may lead to pipe formation and an eventual largescale failure (not specific to bogs).  Clay alter the chemistry of bog waters (see 4.4) affecting the survival or recolonisation of desirable bog species as well as being detrimental to archaeological remains (see 1.6).  Clay bunds have to be built onto mineral rather than peat substrates, as peat is too unstable to support the weight of a clay bund. However, clay bunds can be used to seal a damaged edge to stop lateral seepage from the edge of a peat body. Note, though, that such constructions alter the natural functioning of a peat body since there would normally be constant lateral seepage (see 2.5, Figure 5.44). Clay for bund construction should be wet, free from woody material and stones and impermeable. The bund is constructed by removing a narrow (1m) trench of peat (where necessary) down to and into the mineral substrate. Clay is then packed into the trench and compacted to force out any cracks or air gaps. Peat should then be added across the top of the clay bund in an attempt to seal in the mineral source (Figure 5.44). It is important to maintain moisture levels within surrounding peat which, in turn, keeps the clay wet. Though re-vegetation of the peat cap should be encouraged, scrub should be prevented from establishing. Additionally, clay bunds can be used to re-create the lagg fen system around a raised bog. Here, the bund is built some way from the bog edge to allow shallow flooding between the peat body and the clay bund. Enrichment of fen waters from the clay is fine provided the water-level is below the bog surface. Vegetation exploiting more nutrient-rich conditions within the fen, such as reed species, are not then able to colonise the peat dome. This approach appears to be working well at Cors Caron.

140


Conserving Bogs

5.1

Methods and techniques for Management

5.1.5 Ditch infilling The lowering of the water-table caused by drainage ditches can be reversed by installing a series of dams (see 5.1.2). However, there may still be greater movement of water though dammed ditches (especially on steep gradients) than naturally within the upper layer of a bog. An alternative approach, therefore, is to infill the ditch completely. This technique has been used at a few sites. From the experience gathered from these limited applications several practical considerations should be borne in mind:  Moving peat alters its physical structure; excessive handling turns peat into a sloppy soup. Consequently, although a ditch may be infilled, it may still act as a conduit for water.

Figure 5.44 Cross section of a clay bund used to reduce lateral seepage at a damaged bog margin.

 Material used to infill should be nutrient poor and relatively impermeable. Dried, oxidised and mineralised peat is unsuitable.

 The volume of excavated peat needs to be greater than the volume of the ditch because of compression and structure loss. The method is limited, therefore, to sites where peat is readily available and its excavation does not compromise conservation objectives (archaeology for example). Wet peat is very heavy and transportation is extremely labour intensive. The use of machinery allows large volumes of peat to be excavated (with minimal disturbance to its structure) and moved with relative ease. As with any use of machinery on site, the impacts to the bog surface in terms of damage should be carefully considered (see 3.3.6, 5.6).

Ditches outside or at the edge of the peat boundary can be filled with materials other than peat (Figure 4.45) although nutrient enrichment problems should be considered. It is particularly important that nutrient enriched water does not back up onto ombrogenous bog vegetation. Bearing in mind the above problems of ditch infilling, the following guidelines are of use:  Clean out the ditch removing any unconsolidated peat or plant material.  Pack the peat into the ditch making sure that no cracks are left. Obvious weakness points are at the ditch walls and base.  As the peat is packed into the ditch it should be compacted down to decrease permeability. A flat "tamper" is should be used in preference to feet.  Fill the ditch until the infill is slightly proud of the bog surface to allow for settling. Figure 5.45 Infilling peripheral ditches with clay  To prevent erosion, the surface should be dressed with vegetation. This is best taken from the original excavation area(s) as sods (Figure 5.46).

(i) before works and (ii) after works.

Only use a wheelbarrow fitted with a balloon tyre when carrying peat. Laying down temporary protection around the excavation point reduces levels of trampling damage. If duckboarding is not available, use wooden pallets. A temporary path between the excavation area and the ditch is useful. 141


Conserving Bogs

5.1

Methods and techniques for Management

ď&#x201A;ˇ Plough drained bogs have a ridge of excavation spoil parallel to the ditch. The spoil can be used as infill. Peat from older spoil is too oxidised (Figure 5.47).

ď&#x201A;ˇ The use of other materials entails the same approach as above. However, the nutrient component of the material should be carefully considered before infilling ditches on the open bog (see 4.4, 4.5). Even if a clay infill is capped with peat, enrichment may still occur changing the vegetation within the immediate vacinity of the ditch.

Figure 5.46 Infilling a ditch with peat taken from an adjacent borrow pit.

Figure 5.47 The comparative efficacy of fresh (i and ii) versus old (iii and iv) spoil as a material to infill a ditch. This technique is amenable to large-scale schemes using wide-track bulldozers to move peat.

142


Conserving Bogs

Methods and techniques for Management

5.2 5.1.6 Pumping Water is vital to any peatland system (see 2.5, 3.1.3) and in special circumstances it may be necessary to supplement the natural supply (from precipitation) with an alternative source by pumping. To maintain or encourage rain-fed vegetation, the water must also be rain-fed (Wheeler & Shaw, 1995). The use of minerotrophic water generally promotes the development of a fen flora. Circumstances in which pumping may be useful include:  the preservation of archaeological artefacts or palaeoecological records (1.6);  the maintenance of waterlevels in open water bodies or ditches (this can be used to artificially raise water levels in peat remnants (Figure 5.48);  temporary measures to kill off unwanted vegetation (usually scrub);  temporary measures during periods of drought; and,  re-wetting - following major management operations.

As with all management techniques, pumping should be carefully considered within the overall management scheme for the site (see Part 3). Pumping water should be viewed as a short-term solution; it is not a sustainable management option. Pumping can usually only be targeted at rather small areas. Consideration should be given to the following: Resources: the technical specification of the pump determines its output and often its price. Depending on specific situations, the pumping scheme may require supervision and staff time.

Figure 5.48 Using a pump to maintain high water levels behind a bund. Water Source: given that, in most situations, the requirement is for rain water, a suitable storage facility is necessary - the volume of water required dictates the size and characteristics of such a facility. Water Quality: even when meteoric water is used - its movement through pumping increases oxygen levels and may lead to increased microbiological activity (Wheeler & Shaw, 1995) which may in turn stimulate the mineralisation of peat. Application: unless the water is pumped into another body of open water or a ditch system, problems may arise at the outflow point through local inundation, erosion or the creation of run off gullies.

5.2 REVEGETATING PEAT SURFACES 5.2.1 Introduction Bare peat surfaces are difficult to re-vegetate because of a variety of inhospitable conditions. The success of any re-vegetation scheme depends upon the following:  Hydrological characteristics (see 2.5, 4.3).

143


Conserving Bogs

5.2

Methods and techniques for Management

 The microclimate of the peat surface. In summer, bare black peat can heat up to over 80ºC (Maas and Sliva, 1984) and the exposed surface is highly susceptible to erosion from frost, wind and rain.  The chemical conditions of the bare peat. High evaporation and an unnatural hydrological regime causes mineralisation and oxidation. Peat extraction may have exposed more mineral-rich sediments further changing the surface chemical properties. The chemical and nutrient status of the peat surface affects the type of vegetation which can colonise it. Oligotrophic bog species are unable to colonise nutrient-rich fen peats for example (Poschold, 1992) although this may be tolerable if the resulting fen acts as a transition to rain-fed bog vegetation in the long-term (Wheeler and Shaw, 1995). Figure 5.49 shows the differing characteristics before and after peat extraction.  The distance from a suitable refugia of bog species and the vegetation composition of that refugia.  The viability of a possible seed bank within the remaining peat.

Whatever the conditions of the bog surface to be revegetated, re-colonisation may need to be accompanied by hydrological management (see 5.1) and must always be carefully planned (see Part 3). It is particularly important to carefully consider after-use conservation plans of sites currently under peat extraction (see 1.8, A1.2) as it is important to plan into extraction activities a safeguarded refugia of bog species to use as a harvesting source for direct re-introduction (see 5.2.3) or for seeds/spores (see 5.2.2). It is also particularly important, in terms of cost and expertise, to plan the final phases of extraction to leave (sculpt) bare peat surfaces which have the maximum potential for re-wetting and re-vegetation strategies (see Wheeler and Shaw (1995) for more detail). Wheeler and Shaw (1995) consider re-naturation of bare peat surfaces in some detail and should be consulted if these approaches are used. However, the main approaches are summarised here. These are natural recolonisation (5.2.2), transplanting whole plants (5.2.3), using seeds and spores (5.2.4) and rafting (5.2.5). The approach used relates to different re-wetting strategies (Table 5.4).

Figure 5.49 The changing environmental conditions at the peat surface following extraction dictates the type and range of species that may colonise the site.

144


Conserving Bogs

5.2

Methods and techniques for Management

Table 5.4 Rewetting strategies and introducing vegetation. Re-wetting Strategy

Introducing Vegetation

Construction of embankments/bunds leading to continual inundation. Initial inundation through sluice control of embankments. Fluctuation may be seasonal (governed by climate) or controlled (by sluices). Strategy aimed at raising levels to surface for all or majority of year. Minimise fluctuation and inundation (mimic "natural" levels).

Rafting of aquatic Sphagnum - introduction of fragments or/and whole plants. Rafting of Sphagnum coupled with "tussock buffering” from cotton grasses and purple moor grass. Individual whole plant/fragments or within turfs seeding/spores of all desired species directly to surface.

5.2.2 Natural recolonization Natural recolonisation of a bare peat surface may occur from a viable seed bank stored within the uppermost layers of peat or from wind-borne spores/seed from adjacent refugia. Ombrotrophic mire species have the capacity to store persistent seed banks (Wheeler and Shaw, 1995). On a small-scale, peat samples can be cultivated in pots or trays to give an indication of the range and abundance of species that are still viable within the seed bank. However, at most peat mining operations, the uppermost layers, which contain the greatest percentage of viable seed, have been removed thereby reducing the potential for recolonisation from this source. Sometimes, the top layers of vegetation and peat are stored prior to commercial extraction to be spread over the bare peat surface, in a thick layer (approximately 30cm), to help facilitate revegetation on cessation of mining. This material is known as bunkerde in Germany. Evidence to support the value of this approach is inconclusive (Wheeler and Shaw, 1995). Another mechanism for natural recolonisation is from wind-borne spores or seeds derived from local refugia. Little is known about either the dispersal capabilities or capacity of the seed to colonise onto bare peat surfaces. The success of natural recolonisation schemes depends upon the factors outlined above (5.2.1). Open water can be colonised by encouraging aquatic Sphagna to colonise (rafting - see 5.2.5). Rafting is the establishment of an initial layer of vegetation onto which successional colonisation of other species takes place. Rafting schemes have taken place with some success and recent paeleoecological histories (Joosten, 1995) would also suggest the approach can work. The exact requirements for this type of successional development, however are, still unknown and it remains an area for further research. 5.2.3 Transplanting Transplanting whole plants onto bare peat surfaces has been tested at Kendmühlfilzen, Gardrum Moss and elsewhere. The following points should be noted:  there may be difficulty in locating a suitable donor site;  there may be unacceptable levels of damage to the donor sites from plant collection;  pioneer or ‘nurse’ species may have to precede Sphagnum re-introduction because the micro-climate is too extreme for Sphagnum recolonisation;  procedures can be very labour intensive;  the technique is unsuitable for large-scale operations; and,  adequate investigation of hydrological and chemical parameters must precede plant introduction.

Whole plants used for colonisation may be either individual specimens or groups moved as turves. Individual plants are best transported and planted as a peat core; this should prevent excessive damage to roots. Tussock species such as hare’s tail cotton grass are best transplanted as juvenile specimens or split into smaller parts from large tussocks. Hare’s tail cotton grass seeds well if it is burnt the year before. Sphagnum has the capability of growing from small fragments of whole plants. However, the success rate 145


Conserving Bogs

5.2

Methods and techniques for Management

of scattering fragments onto bare peat is governed by the microclimatic characteristics at the surface. Small fragments or juvenile plants are very susceptible to drought and do not possess the water-retentive abilities of larger hummocks. If the surface is not initially suitable, Sphagnum should be introduced either in conjunction with ‘nurse’ species or in larger peat turves (e.g. Sliva et al., 1996). The translocation of vegetation in turves is the most practical way of introducing whole plants onto a bare peat surface. This method has not been fully tested for bogs. However, on heaths, young heather stands have been successfully translocated using a turfing machine (Gimingham, 1992). The turves are cut in 1m wide sections to a minimum depth of 5cm, rolled up and transported to the receptor site. Older heather stands have been moved in larger turves cut with an excavator. At the receptor site the large turves are placed in shallow trenches and the gaps between the turves infilled with peat and heather cuttings (Gimingham, 1992). Other species can be also translocated in turves. Turves containing cotton grasses or purple moor grass should be cut to a depth of approximately 30cm (Figure 5.50) or one spades depth. This provides adequate protection to the root stock and reduces stress during and after translocation. Sphagnum is probably best introduced by this method. There may be an advantage in incorporating ‘nurse’ species within a Sphagnum turf to ensure more amenable micro-climatic conditions at the receptor site. However, this should be weighed-up against the possibility that the ‘nurse’ species may out-compete the Sphagnum. The physical, hydrological and chemical conditions at the receptor site must suit the growing requirements of the translocated species. An important benefit of transplanting species within turves is that soil micro-organisms and ground invertebrate communities are incorporated.

Figure 5.50 Species can be introduced in turves or directly to the surface. Initially growing nurse species such as Eriophorum vaginatum can help to maintain a more suitable microclimate for Sphagnum colonisation. 5.2.4 Seeds and Spores Where local refugia exist (there is little knowledge about quite how local it should be) and prevailing conditions are appropriate, recolonisation from seeds and spores may be possible. Unfortunately, little is known about the capabilities of different Sphagnum species to colonise bare peat or open water from spores. However, dammed ditches are rapidly colonised. Vascular species (e.g. ling heather and hare’s tail cotton grass) have been studied in more detail, their colonisation of bare peat surfaces can be rapid, but may not be desirable. Birch and bracken can be particularly difficult management problems should they colonise bare peat surfaces. In most cases, such colonisation, it is a reflection of the physical (hydrological and chemical) regime of the exposed peat surface. Areas may be deliberately seeded using seed from local sources. Seeds of local provenance are preferable but care should be exercised as such stocks may also include unwanted or inappropriate species. Some species, such as heather, may be available as part of commercial seed mixes. Given the difficulties inherent 146


Conserving Bogs

5.2

Methods and techniques for Management

to covering large areas, planting (see 5.2.3) or seeding numerous small areas to act as a nuclei for natural recolonisation (see 5.2.2) is advisable. 5.2.5 Rafting

Rafting is usually associated with the re-vegetation of a post-extraction surface (i.e. oxidising bare peat). Bunds are constructed (see 5.1.4) and the surface is flooded to encourage the colonisation of aquatic Sphagna (e.g. Sphagnum cuspidatum) to form floating rafts. Eventually, successional colonisation by terrestrial Sphagnum species may take place. If the growing raft meets the surface, peat may start to accumulate and some of the functions of the acrotelm may be restored. Practical considerations include:  Maintaining a flooded surface all year round may require bunds or embankments.  If the water level drops below the surface (see 4.3.3), for any considerable time, colonising vegetation may be prone to desiccation.  Water chemistry must be suited to colonising species (see 2.6, 4.4). A settling period of at least 12 months should precede any vegetation introduction.  Large open water bodies may attract considerable numbers of wildfowl. This can lead to eutrophication and disturbance which are detrimental to Sphagnum growth.  Large open water bodies are affected by wave action which deters Sphagnum growth (see Figure 5.51).  There is no guarantee that terrestrial Sphagnum species will colonise a floating raft.  Observations from a number of sites have shown that 'weed' species such as birch may colonise the floating raft.  If Sphagnum does not already exist in wet hollows or ditches it can be introduced as whole plants or fragments from a suitable donor site (see 5.2.3).  Water levels should remain above the surface (maximum 50cm) for the entire 12 month period (see 4.3.3).

Figure 5.51 Large open water bodies are unsuitable for Sphagnum recolonisation because of disturbance from wildfowl and wave action (Yorkshire Dales, UK). Sphagnum communities, which existed in wet hollows prior to inundation, may float up to the surface with any loose material and start to grow. If, however, Sphagnum was not found before inundation, it may need to be introduced. The most successful coloniser of open water is Sphagnum cuspidatum which can be introduced as whole plants or mashed up and introduced as fragments (Money, 1994). Other aquatic species, Sphagnum recurvum and Sphagnum auriculatum, do not regenerate so well and it may be more prudent to introduce these species as whole plants (Wheeler and Shaw, 1995). 147


Conserving Bogs

Methods and techniques for Management

5.3 A food blender can be used to thoroughly mix up fragments prior to dispersal. A soup of different species can be made, depending on prevailing conditions and availability. To aid initial colonisation, scrub brashings or similar can be thrown into the open water. These may then act as a protective and binding framework for Sphagnum to colonise over. This technique can also be useful in minimising wave action. Rates of colonisation are variable. If the conditions are amenable to Sphagnum growth, colonisation can be rapid although successional colonisation of other Sphagnum species, such as Sphagnum magellanicum or S. papillosum appears to be slow. At Bargerveen, successional colonisation has been very slow even though a thick (> 50cm) skin of S. cuspidatum and Sphagnum recurvum has already established. Conversely, other sites such as Wieninger Filz in Germany demonstrate rapid successional ombrotrophic re-vegetation. Variation in the rate and success of succession relates to:  distance from refugia;  inability of species to colonise over aquatic Sphagnum;  nutrient status of either rainfall or groundwater; and  fluctuating water levels or prolonged grounding, and therefore drying, of the Sphagnum raft.

5.3 MANAGING SCRUB AND TREES 5.3.1 Introduction Where the climate is dry enough - central Europe for example - trees are a natural element of bog flora. Even in oceanic Britain, studies have shown, that, in the past, trees have grown naturally on bogs (for example, Chambers, 1996) during climatic warm periods which allow trees to become established (Barber et al., 1994). Today, many sites are subject to scrub or tree invasion because of various human related activities (see 1.14). Often, scrub is controlled through grazing and burning (Smout, 1996) leading some writers to suggest that trees are unnaturally absent from some British bogs (Ingram, 1996) Scrub invasion, once initiated, tends to succeed towards woodland because:  Established scrub and mature trees intercept rainfall in the canopy before it reaches the bog surface. A proportion of this rainfall is then lost to the atmosphere through direct evaporation. Scrub and trees also have higher transpiration rates than bog vegetation. Hence total evapotranspiration is enhanced considerably.  Drying of the peat surface stimulates the release of nutrients locked in the peat which encourages the process further.

The pattern of encroachment shown in Figure 5.52 is typical. Note that, whilst succession to closed canopy woodland is not uncommon, the ground flora often indicates the sites’ boggy past - still dominated by Sphagnum mosses (especially S. palustre) - as the substrate is still peat. Impacts of scrub encroachment are shown in Table 5.5.

148


Conserving Bogs

5.3

Methods and techniques for Management

Table 5.5: Impacts of Scrub encroachment Species

Conditions for Establishment

Silver birch (Betula pendula) & Downy birch (Betula pubescens). Seeds ripen between July & August - shed between September & November germination in the field between April & June. Good coloniser of open, bare ground - coppices when cut. Scots pine (Pinus sylvestris) Seeds take three years to mature on tree - released in March - April. Tolerant of wide range of habitat. Does not coppice when cut.

Lowered watertable, disturbance of bog surface creating open areas of bare peat. Nutrient enrichment or flushing. Seed source. Lack of grazing.

Rhododendron ponticum. Prolific seed production establishes well on bogs - shade tolerant with potential for rapid growth. Ability to coppice when cut.

Impacts with Age Sapling Impacts are minimal when trees are < 20cm tall though root system may already be extensive.

Light scrub Five year old trees affect immediate area around the base of the tree by drying and shading. Increases seed source.

Established Scrub Vegetation change across a larger area due to increased evaporation and interception losses. Shading and nutrient enrichment increases. Invertebrate and bird populations change.

Dense scrub Physical changes in peat due to compaction and disturbance from root systems around the base of the tree. Impacts from nutrient release & shading limited to immediate area. Large seed source.

Mature Trees Majority of vegetation shaded out. Bare oxidised peat surface. Cracking around base & roots. Shrinkage of peat. Invertebrate and bird populations now solely woodland communities.

Lowered watertable, disturbance of bog surface creating open areas of bare peat. Seed source.

Impacts are minimal when trees are less than 20cm tall. Roots still shallow.

Vegetation change to drier communities around individual trees.

Vegetation change across larger areas, switch to Calluna dominated communities. Invertebrate and bird communities change.

Sphagnum may still be present in open areas. Physical changes in peat due to compaction and disturbance from root systems around base of tree. Increased seed source.

Even a small decrease in water-table makes a habitat suitable for establishment. May establish quickly from local seed source.

Impacts minimal although growth may be rapid.

Quickly forms dense shading over ground flora to reduce cover of shade sensitive Sphagnum species.

Shades out bog species entirely from dense growth of bushes - may increase acidification of surface from leaf litter. Prolific seed production 2mx10m bush can produce over 1million seeds.

Tends to cover ground entirely from many separate root stocks. Shades out all other species to leave bare peat surface may remain wet.

Sphagnum recurvum dominant species in wet open areas, dry areas dominated by heath communities. Oxidation, shrinkage and cracking of peat. Woodland invertebrate and bird communities. As dense scrub.

To control scrub it is necessary to establish the root cause of the problem (Rowell, 1988). There is little point in expending considerable resources on scrub removal to find that the problem simply re-occurs. If trees have established in response to a lowered water-table, efforts should be made to re-wet the site. Any scrub clearance measures should be incorporated into a comprehensive site management programme (see Part 3). Methods for removal include:  hand pulling (5.3.2.1) for seedlings and saplings;  cutting with bow saws (5.3.2.2) or brush cutters (5.3.2.3) whilst for young trees; and  chain sawing (5.3.2.3) for mature trees.

It is important is to clear scrub and trees as quickly and safely as possible minimising disturbance to the bog surface. Some species coppice when cut and require secondary treatments such as re-cutting (5.3.3.3), flooding (5.3.3.4) , grazing (5.4) or chemical applications through spraying (5.3.4.2), weed wiping (5.3.4.3) of the new growth or painting of the cut stumps (5.3.4.4). Once scrub is cut, it is often removed - difficult on large sites and/or with large volumes of material (5.3.5). 149


Conserving Bogs

5.3

Methods and techniques for Management

5.3.2 Cutting and Felling 5.3.2.1 Hand pulling For small saplings and seedlings, hand pulling is an effective method of control although it is labour intensive. Disturbance of the ground is the biggest problem associated with this technique. It is useful to adhere to the following guidelines:  The best time to pull young trees is when the ground is least susceptible to trampling damage - during summer when water-levels are low or in winter during mild frosts. Resulting disturbed ground may be seeded by neighbouring trees at certain times of the year (September-October for birch and February-March for rhododendron).  Areas for scrub clearance should be specified within the management plan (or annexes) for the site (see Part 3). It is useful to mark areas out with canes and tackle in an orderly manner - a ‘police type’ sweeping line is useful to ensure areas of scrub are not missed and to help accurate record keeping (Figure 5.53).  When pulling seedlings, reduce damage to the surface, by placing the feet as close as possible on either side. This prevents Sphagnum hummocks being pulled up with the root systems. (Figure 5.53).  Seedlings can either be left on site or collected in sacks. Remove the plants more carefully if they are to Figure 5.52 A typical pattern of scrub be used elsewhere or sold. encroachment on a drained and cut raised bog  If there is a possibility of disturbing archaeological remains then do not pull.

5.3.2.2 Hand Sawing Hand sawing of trees is common - see Brooks (1980) for a detailed account. On bogs, consider the following when sawing:  Trees that coppice require after-treatment (herbicides) following felling. To relocate cut stumps, it may be useful to cut the tree high, leave the stump visible, then come back on another day, cut to ground-level and treat.  For non-coppicing trees (pine), cut as low as possible to allow Sphagnum to grow over the stump. Birds use stumps for perching which can local enrichment.

150


Conserving Bogs

Methods and techniques for Management

5.3

Figure 5.53 Working in a line is the most efficient way of hand pulling tree saplings and seedlings. 5.3.2.3 Brush Cutter and Chainsaw Felling. For larger trees, chain saws are the best option although these instruments should not be used without adequate training - see Brooks (1974) for full details. The Forestry Safety Council have produced leaflets which highlight the safety issues inherent in chainsaw use. Poor terrain and difficult access on many bogs accentuates the need to strictly follow all health and safety guidelines. 5.3.3 Scrub Control without Herbicides

5.3.3.1 Introduction The use of herbicides should be avoided where possible in line with precautionary principles - the long term effects of substances like herbicides are not yet known. There are a number of techniques that can be employed to control scrub without resorting to herbicides. These are ring barking (5.3.3.2), cyclical cutting (5.3.3.3) and flooding (5.3.3.4). 5.3.3.2 Ring barking Ring barking can be used to kill a tree in-situ. A section of bark is cut away with a bill hook around the whole circumference of the trunk. This severs the vessels in the cambium and xylem which are responsible for growth and the transport of nutrients between the leaves and the roots. The process is simple and, when conducted properly at the appropriate time of year, effective. There are, however, several factors to consider: ď&#x201A;ˇ To secure the death of the tree, a section of at least 12cm (for birch and pine species) must be removed down to solid wood. Smaller sections of 3-5cm can heal over, and the tree may eventually recover. ď&#x201A;ˇ

The timing of ring barking is important. The tree should be cut immediately after it has set seed (see Table 5.4); cutting before this induces the tree to produce more seed.

151


Conserving Bogs

5.3

Methods and techniques for Management

5.3.3.3 Cyclical cutting Once a tree is felled, continued cutting of re-growth eventually kills it. Though effective, this method is labour intensive and is not really suited to large areas or quantities of scrub.  Strip the newly grown shoots with a bill-hook or similar bladed tool. The more damage to the stump the better as this encourages infection and further stress. It is important to cut-back all re-growth including any basal buds which are starting to form.  The same treatment should follow in subsequent years. Most species die after approximately five years from this kind of treatment (Crofts and Jefferson, 1994). Given the difficulties in re-locating cut stumps, one should expect a lower percentage kill rate than would be expected using chemicals.

5.3.3.4 Controlling Scrub by Flooding Depending on the species, soil and water conditions, scrub can be killed by raising water-levels. Some species can tolerate wet conditions and raising water levels back to the surface (i.e. approaching natural conditions) may only slow down growth (Figure 5.58). Birch and willow, in particular, are capable of surviving waterlogged conditions for most of the year. Flooding for the entire year is more effective. This may necessitate the construction of bunds to impound water (see 5.1.4). Where water levels can be controlled, through the manipulation of sluice gates (see 5.1.3) within bunds levels can be dropped after the scrub has been killed. An advantage of killing scrub by this method is that when the tree eventually falls (into the open water), it acts as a temporary framework for establishing aquatic Sphagnum. Dead wood also decreases wave action which in turn aids Sphagnum development (see 5.3.1). Flooding can be also be employed to control re-growth by diminishing a tree’s chance of recovery through coppicing.

Figure 5.54 Some trees may be able to survive when water levels hae been raised through hydrological management. Kill rates are improved when water levels are raised above the surface and can be maintained throughout the year.

152


Conserving Bogs

5.3

Methods and techniques for Management

5.3.4 Scrub Control with Herbicides 5.3.4.1 Introduction The control of invasive species may require herbicides. These can be applied directly to the leaves, applied to the trunk or painted onto the cut stump. Their use should be carefully controlled both for health and safety reasons and so as not to affect non-target species. Herbicides should only be used if absolutely necessary (see 5.3.3) as the fate of these herbicides in peat is unknown. 5.3.4.2 Chemical Spraying As the long-term effects of spray drift on vegetation and invertebrates are unknown, large scale spraying should be avoided as a means of controlling scrub. However, studies on drier heath communities suggest that foliage spraying of either saplings or re-growth of cut stumps is effective and the effects on non-target species are comparatively minor. Krenite (fosamine ammonium) appears to have limited effects on ling heather (Marrs, 1985). Glyphosate, if administered in weak solution in May-June, also appears to have a limited influence on non-target species (Gimingham, 1992). In these studies, however, non-target species are defined as dwarf shrubs rather than mosses. The use of a drench gun to administer a measured dose of herbicide to a small surface area reduces the risk of large scale over-spray. Alternatively, weedwiping (see 5.3.4.3) can be used. Both fosamine ammonium and glyphosate have British government approval for use with drench-guns. Using a drench gun to treat cut stump regrowth with fosamine ammonium: Fosamine ammonium should be applied to all visible foliage two months before leaf fall. The herbicide is absorbed through the foliage, stems and buds of treated plants and effectively prevents bud formation the following year. Spraying should take place in dry weather allowing 6 rainfall-free hours before and 24 rainfall-free hours after application (Marrs, 1985). A non-ionic wetting agent (e.g. Agral) mixed with the standard fosamine ammonium and water solution (follow product label guidelines) may enhance herbicide performance on birch. A kill rate of up to 90% has been recorded for this method (Marrs, 1985). Note that fosamine is difficult to obtain and is costly. Using glyphosate to treat cut stumps with a drench gun: Treatment must be during dry weather otherwise the herbicide may wash off before being absorbed into the leaves. Always spray systematically by following a pre-determined route preferably using a marked grid. This ensures all areas are covered and helps to evaluate management; grid references can be recorded with dates, times, weather conditions, herbicide solutions etc. June and July are the best months for treatment (Tabbush and Williamson, 1987). Not all the re-growth from individual trunks needs to be covered as the herbicide is systemic. If treating rhododendron the additive High Trees Mixture B (at 2% of spray volume) should be incorporated within the solution (mixed to labelled guidelines). 5.3.4.3 Chemical Application by Weedwiping A weedwiper consists of a rope wick attached to a reservoir handle (Figure 5.55). Herbicide solution, in the handle, impregnates the wick which is then brushed over the target vegetation. Calibration of the weedwiper depends upon herbicide solution concentration (follow manufacturer's recommendations on the label) and the flow rate from the handle to the wick can be adjusted. It is important that a constant flow to the wick is maintained.

153


Conserving Bogs

Methods and techniques for Management

This method is particularly useful on peatland sites where it is still unclear of the effects that non-selective herbicides have on the specialist flora and fauna. Glyphosate is recommended for use with weedwipers. The procedure is as follows:

5.3

 Work out a systematic pattern to work across the bog. Treat each area thoroughly before moving onto the next area. 

Use glyphosate (Roundup) in solution of 12-18% in water (Cooke, 1986) with an appropriate colour dye.  Apply herbicide whilst target species is actively growing and in leaf.  It is not necessary to cover all of the plant, as glyphosate is systemic; partial coverage effectively kills re-growth from cut birch stumps.  Avoid contamination of non-target species; glyphosate is non-selective and affects all contaminated vegetation.

Figure 5.55 A weed wiper, used to apply herbicide to leaves and re-  Ensure wick remains wet throughout application. growth.  Follow manufacturers guidelines for the safe use of the chemical and its

Food colouring can be used as a cheap alternative to specialist dyes. Change the colour of the dye each year to help determine success rates over time. disposal.

5.3.4.4 Herbicide Application by Painting Cut Stumps This method of herbicide application is favoured on peatland sites as the risk of contaminating surrounding vegetation is low. British government approval has been given to application of glyphosate (Roundup) and triclopyr (Garlon) by painting. The technique is not always effective especially where treatment does not immediately follow cutting and/or it has rained before, during or after treatment. However, provided suitable conditions exist, kill rates for birch and rhododendron can be up to 90%. A good success rate has been reported if the regrowth is treated in the spring following cutting (i.e. just as the dormant buds are sprouting). It is important that adequate planning is undertaken before any practical work starts. The areas to be treated should be identified on a site map and preferably marked on the ground with canes. Establishing a grid system is the most common method for dividing up a site. By doing this, work is concentrated in small zones rather than dispersed across the whole site and recording management operations is easier. Figure 5.56 shows the procedure for use although bear in mind the following:

154


Conserving Bogs

Methods and techniques for Management

5.3

Figure 5.56 When applying herbicide to cut stumps, follow a standard procedure.

ď&#x201A;ˇ Avoid treating a tree when its 'sap is rising' (i.e. just before and whilst the tree is in leaf) - this deters absorption of the herbicide into the cut face. ď&#x201A;ˇ Cutting and treatment should be done on the same day. If this is not possible (for example, it starts to rain) then cut the stems high above the surrounding vegetation, return, cut low and treat.

Preferably, do not separate the cutting process from the painting. Work in teams of 3-4, with one person painting whilst the others cut. Even though this method is labour intensive it is more efficient as it reduces the number of stumps that are left untreated. ď&#x201A;ˇ Treatment should always take place during dry weather and, to allow the solution to be taken-up, a dry spell of at least 24 hours should follow.

155


Conserving Bogs

5.3

Methods and techniques for Management

5.3.4.5 Application of herbicide to standing trees Spraying (see 5.3.4.2), weedwiping (see 5.3.4.3) and painting of cut stumps deal effectively with the problems of re-growth following cutting. However, where the objective is to kill a standing tree, other methods are employed. Ring-barking (see 5.3.3.2) and flooding (see 5.3.3.4) are useful approaches though not always successful. Herbicide application may be necessary in which case frill-girdling, notching and drilling are used. Note the following advantages and disadvantages: Advantages  Problems associated with disposal of cut material from remote or difficult locations are avoided.  Waste disposal damage (see 5.3.5) is avoided.  Dead trees provide an excellent habitat for invertebrates and birds. Disadvantages:  Dead trees are potentially hazardous. Dead trees should be felled where there is public access.  Large or particularly dense areas of dying trees may alter the nutrient status as they decay.  If trees are stressed they produce a larger number of seeds.

Frill-girdling: A frill girdle is prepared by making a series of overlapping downward sloping cuts at the base of the trunk with either a light axe or bill hook (Figure 5.57). The cuts should be deep enough to penetrate the cambium allowing effective absorption of the herbicide. Ammonium sulphate (Amcide) crystals at 15g/25mm trunk diameter (Cooke, 1986) should be packed into the cuts. It is important that herbicide application immediately follows cutting. Best results are obtained from applications made during June - August. Application must be during dry weather as crystals dissolve in water and wash out of the cuts. Notching: Notching is similar in principle to frill-girdling and is the recommended method for dealing with large trees in-situ. A series of evenly spaced pairs of downward sloping cuts are made around the full circumference of the tree, as close to the ground as possible (Figure 5.57). Ammonium sulphate crystals (15g/notch) should then be packed into each notch. Application should only occur during periods of dry weather as crystals dissolve in rain and wash out of the notches. The best time for application is June - September. On larger trees a second application may be necessary. Drilling: An alternative to notching is drilling (Figure 5.57). Holes should be at least 25mm diameter and penetrate into the trunk Figure 5.57 Standing trees can be killed by up to 75mm. Ammonium sulphate crystals are packed into by frill-girdling, notching and drilling the holes. Once the crystals have been packed into the holes, plug the holes with stone, bark tape and so on, to prevent the crystals dissolving and washing out in the rain.

156


Conserving Bogs

5.3

Methods and techniques for Management

5.3.5 Waste Disposal 5.3.5.1 Introduction Removing scrub and cut timber waste from bogs presents numerous difficulties and is a common management problem, especially where large volumes of material are involved. Leaving the brash on site can lead to localised enrichment, shading out of intolerant species and also represent a significant fire hazard. Table 5.5 details some of the techniques that have been employed. Table 5.6 Methods of Felled Tree and Scrub (Waste) Disposal Approach

Resource Requirements

Site Requirements

Comments

Leave on site (stacked).

No direct costs other than labour.

Best suited to large sites with zones of dense scrub and where options for disposal are limited

Could be a fire risk and also lead to localised enrichment. Best to stack material as it is cut. Avoid dragging scrub long distances.

Leave on site (unstacked). 5.3.5.2

No direct costs - other than those associated with felling.

Best suited to large wet sites where scrub is distributed widely in low densities.

Where wood is in full contact with the surface of the bog - Sphagnum quickly covers it. Minimal extraction damage.

Leave on site in ditches. 5.3.5.2

Small cost implication, labour intensive if large volumes of waste are to be disposed of.

Open ditches or flooded lagoons.

Scrub can act as a framework for Sphagnum growth in ditches - scrub also impedes flow (but does not act as a dam). This is the best option for on-site disposal.

Drag to the edge of the bog. 5.3.5.2

Small cost implication, can be very labour intensive. May require temporary boardwalk sections.

Inappropriate on large sites due to dragging distances.

Can cause damage to sites from trampling and dragging over sensitive areas. This can be reduced by laying temporary boardwalks.

Burning on site. 5.3.5.3

Relatively small cost implications - labour dependent on scale of operation.

Best suited to larger sites.

Risk of fire, local enrichment and scorching of bog surface.

Chipping on site. 5.3.5.4

Cost of purchase/hire of chipper + means of moving chipper. Labour resources dependent on scale of operation. Possible revenue from sale of chips.

Can be utilised on large and small sites. Chippings may still have to be removed.

Chipping waste reduces volume. It still requires the chippings to be disposed of. Adequate provision for transporting chipper may lead to damage of bog surface.

Helicopter off site. 5.3.5.6

Extremely expensive to hire helicopter. Labour required to prepare waste for uplift. Possible revenue from sale of timber.

Appropriate for large sites or sites with very poor access.

Due to associated expense, adequate planning should be used. Only an option in limited circumstances due to excessive costs.

ATV extraction. 5.6.9

High labour requirement for preparation of material. Cost of purchase or hire of suitable ATV.

Best suited to drier sites capable of sustaining vehicle use. The relatively small payload means many journeys are required.

Where dragging by hand is the only alternative, the use of ATVs may actually reduce damage to the bog surface. Ideally temporary tracks should be laid down for the duration of the operation.

Winch off site. 5.3.5.7

Cost of winch/block and tackle. Labour resources reasonably small. Possible revenue from sale of timber.

Not appropriate on large sites.

Risk of damage to bog surface from dragging. Dependent on skilled labour to safely operate winches and pulleys.

Standard commercial forestry equipment.

High cost and skill demand, although output is considerable.

Only suitable on damaged sites or those under commercial forestry.

Standard machines (forwarders and harvesters) are too big and heavy to work on bog surfaces without causing extensive damage or jeopardising the safety of the machine. Standard practice on deep peat is to work over a brash mat laid down by the harvester.

157


Conserving Bogs

5.3

Specialist machines, e.g. Vimek Minimaster 101. 5.3, 5.8

Methods and techniques for Management Initial purchase or hire costs significant, although, as with a helicopter or standard extraction machines, a high output can be achieved. A trained operator is required.

Can be utilised on a broad range of sites. Low ground pressure vehicles are specifically designed to work on wet sites.

These types of machines offer good potential for effective removal of timber with minimal damage to the bog surface. Even though ground testing has been very limited, this approach does appear to address many common problems associated with timber extraction from bogs.

The effects of enrichment from leaving cut material on site has yet to be fully determined. Impacts from shading are clearer. Heavy localised shading from a wood pile, for instance, kills many species, in particular Sphagnum mosses. Therefore where large volumes of material are being cut it is advised that the majority of it is removed from the bog surface. Many of the techniques detailed require material to be dragged either off the bog or to a central point for burning, chipping or stacking. Dragging heavy branches and trampling by people soon damages Sphagnum-rich areas. At its most severe, trampling and dragging leads to bare peat surfaces ideal for colonising birch (Atkinson, 1992). When birch is in seed (June-October), well intentioned but unplanned scrub removal may even worsen the situation by encouraging rapid birch colonisation. If these types of approaches are used temporary tracks should be laid to help protect the bog surface. 5.3.5.2 On-Site Disposal The effect of leaving waste on site is now being explored using permanent plots incorporating a number of different species within a broad range of environmental variables (SWT, 1994); this has provided some useful information on short-term vegetation changes. Initial findings have shown that dead wood was rapidly covered by vegetation when it is predominantly in contact with the bog surface and Sphagnum is the main constituent of the vegetation. Where the material is piled up (i.e. not in contact with the surface) or the surface is dry there is little opportunity for colonisation. The best locations for disposing scrub on-site are blocked drainage ditches or open water bodies (man-made not natural pool systems). The brash acts as a framework for Sphagnum to grow over and is particularly useful in deeper water bodies where Sphagnum is slow to colonise. Semi-submerged brash may also suppress wave action across large open water bodies (see Figure 5.58). 5.3.5.3 Burning Waste A common method of disposing of woody material on non-peat habitats is to burn it on site (Brooks, 1980). Risks: On peatland sites, the following should be considered: ď&#x201A;ˇ Always plan emergency measures before burning - contact the local fire brigade for example (see 3.16). ď&#x201A;ˇ Consider burning in frosty weather so that should the fire spread, the damage is curtailed, or wet weather to reduce the chance of a fire getting out of control.

Figure 5.58 Throwing scrub into open water suppresses wave action and can act as a framework for Sphagnum growth ď&#x201A;ˇ Avoid burning directly on the bog surface itself. As well as burning off original vegetation and enriching the area with potash, there is a possibility of igniting the peat itself. Once alight, peat is difficult to extinguish. Fires can smoulder for months, burning slowly beneath the surface, resurfacing considerable distances from the original source.

Dig a temporary circular ditch, or mow a firebreak around the fire to isolate and stop it spreading (Rowell, 1988)

158


Conserving Bogs

5.3

Methods and techniques for Management

 Some damage to the bog surface, from ash enrichment and especially trampling, is bound to occur even if protection (see below) is used.  Ash is a concentrated fertiliser on a bog and must be removed from the bog.  Surface burning may be deleterious to surface and near-surface archaeology.  Always have beaters at hand in case the fire gets out of control.

A useful technique for avoiding some of the problems of burning is to employ a raised burning bin. The bin is raised above the surface to counter scorching, can be moved around the site and the ash can be left to cool down safely before removal. A burning bin is used in the following way:  Locate the bin in the centre of the cleared area close to the wood piles. Choose a position where the bog surface has already been damaged. Areas immediately around large stumps are ideal. Avoid wet areas that would be quickly damaged by trampling (Figures 5.59).  Protect the surface of the bog by placing fire blankets or corrugated sheeting on an area which is 40cm wider than the bin base on all sides.  The base of a semi-portable bin should not exceed 3m x 2m (larger bins become too heavy to lift).

Figure 5.59 Position the bin centrally within the working area. Avoid wet areas which are more  Using one large sheet, or several smaller sheets riveted together, prepare the bin base. Drill 3-5mm holes, 2cm in susceptible to trampling damage

from the edge, at regular intervals around all sides of the bin (Figure 5.60).  Construct a platform for the bin base on top of the fire blanket (metal buckets and log sections have both been used successfully in the past). This creates an air gap beneath the bin base to further reduce scorching of the bog surface (Figure 5.61).  The next stage is to construct the sides of the bin. These contain the fire and stop it and the ash spilling over onto the bog. The sides should fit just inside the bin base (directly in front of the base holes) giving a 2-3cm overlap. Drill 3-5 mm holes to line up with the holes on the base. Holes should also be drilled up the side of the sheets to allow them to be joined together. Join the corners of the sides and the sides to the base by Figure 5.60 Corrugated metal sheets or fire threading pieces of wire through the pre-drilled holes blankets should be laid directly onto the bog and twisting the ends together (Figure 5.62). surface

Lay duckboarding or metal sheets up to and around the bin to protect the most heavily trampled areas.  Once the fire is established (the gaps between the base and sides should provide an adequate draught), designate one person to manage the bin. Do not let the fire rage uncontrollably. Always have a spade available (to dig a trench if the peat catches fire) and a fire beater. Allow at least one hour for the fire to die down. Never leave the fire burning in the bin unattended.  When the fire is "safe" place a lid, constructed in a similar fashion as the base, on top of the bin. This can be weighted down with heavy logs to stop it blowing off with the wind. Left overnight, the ashes are warm the next day. A fire can easily be restarted on the embers. Collect the ashes for disposal (the ashes can be used as a garden fertiliser), once they have cooled before moving the bin. The bin can be moved by sliding 2-3 long lengths of wood underneath to provide a platform. A 1.5m x 2.5m bin can be easily moved by 4-6 people. Alternatively, the bin can be constructed

159


Conserving Bogs

5.3

Methods and techniques for Management

with handles on the sides or attached to the base. Instead of joining the sheets with wire, a system of hinges or brackets can be used enabling the bin to be collapsed for transportation.

Figure 5.61 An air gap, created by raising the bin on blocks, helps to reduce scorching of the surface

Figure 5.62 The finished burning bin. It is important to protect the immediate area around the bin from trampling 5.3.5.4 Chipping Waste Chipping reduces the volume of timber waste produced by scrub clearance operations reducing impacts to the surface from dragging (see A1.6.5) and trampling. An associated benefit of chipping timber is that it produces a useable or saleable commodity. Wood chippings are used as a horticultural mulch or top dressing for footpaths. Alternatively, shredded material (including leaves) is used as a basis for an organic compost (a good peat alternative). Consider the following:  Access to and on the site is important. Larger chippers require a vehicle, preferably an all terrain vehicle (ATV - see 5.6.9), to tow and manoeuvre them around the site. Some sites may have steep slopes or wooded fringes which hamper access.  Impacts to the surface increase with the size and weight of the machine. Balloon tyres can be fitted to reduce impacts (but may require specialist customisation of wheels and axles). Temporary tracks or roads (see 5.6.8) can be laid down to allow the chipper to be easily towed with minimal impact to the surface of the bog. Relatively short sections of track can be laid down, either directly onto the surface or on-top of a brash carpet. The track is moved forward as required (Figure 5.63).  Once the brash has been chipped there still remains the problem of disposal. Options are to remove by vehicle (preferably along temporary access routes - see 5.6.9), by helicopter in bags (see 5.3.5.6) or to leave on-site (see 5.3.5.2).  All the chippers mentioned are fitted with a rotating discharge chute. If the chippings are being bagged an extension to the chute may be required to feed chips directly into the bag.  Chipping off-site is an option where access is restricted, potential damage to the surface is unacceptable or the material is derived from the edge of the bog.  Short term hire or lease of the machine is probably more cost-effective than purchase where volumes are low to moderate.

160


Conserving Bogs

Methods and techniques for Management

5.3

Figure 5.63 Particularly on very large sites, it may be appropriate to chip cut material on-site. 5.3.5.5 Dragging Scrub Off-Site Dragging scrub off site is cheap (when using voluntary labour) though labour intensive and can significantly damage the bog surface. The following guidelines should be considered:  Dragging distances should be kept to a minimum. People soon become bored and tired if distances are over 40m.  An appropriate disposal point is required. The best place to dump cut scrub is in open ditches, either on site (see 5.3.5.2) or at the edge. If there are no ditches on site, scrub should be stacked off the bog, avoiding other areas of conservation interest.  To reduce trampling, distribute the scrub around the periphery rather than dumping at one spot.  Avoid dragging over wet areas.  Reduce damage from dragging by bundling scrub waste within a heavy tarpaulin sack (Figure 5.64). The tarpaulin is dragged over the surface by two to four people.

Figure 5.64 A large sheet or tarpaulin can be used to drag scrub over a site. Using this method more material can be moved in one go, which, in turn, minimises damage from trampling

5.3.5.6 Removing Trees by Helicopter Introduction Despite the high cost of helicopter hire (c.£700 per hour), it can be cost effective to remove large volumes of trees and scrub. The following guidelines are of use:  Cut material should be stacked and packed before uplift and in accordance with the capabilities of the helicopter.  Know the operational limitations of the helicopter: its payload and re-fuelling requirements. An initial site-visit with the helicopter pilot is essential. The dumping zone and re-fuelling area should be inspected.  The number of ground-workers should be kept to a minimum when the helicopter is in the air. Those that are present should be suitably briefed on the necessary safety procedures.  Local residents should be informed of the intended scheme.  Choose a dumping zone as close to the uplift area as possible to reduce helicopter time.  Operational difficulties such as dropped loads, refuelling etc. are bound to occur. Before commencing work, assess likely difficulties and incorporate into the wording of any contract with the helicopter company.

161


Conserving Bogs

5.3

Methods and techniques for Management

ď&#x201A;ˇ Weather conditions dictate helicopter use, so it is important to make contingency plans to account for any bad weather. ď&#x201A;ˇ Using helicopters to remove scrub or trees off bogs is a newsworthy event - contact local media.

Removing Scrub and Brash Prepare forestry nets, such as those used to lift Christmas trees, before cutting scrub. Special attention should be given to the attachment points. There should be at least four on every net with one at each corner. Loops are directly attached to the helicopter or used to hold a long strop which is then attached to the helicopter remote release mechanism (Figure 5.65). A strop (looped at both ends) is fed through the net loops and then the other loop of the strop. The strop loop is then attached to the remote release. The strop is released with the net at the drop off point. There need to be enough strops to cover all the nets or enough to allow the helicopter to fly continually (i.e. until it requires re-fuelling). The added expense of the extra strops is justified by reducing helicopter waiting time during loading and unloading. To remove the maximum amount of scrub in the minimum number of nets, scrub should be cut up into small sections. Time spent on compacting the scrub into the nets is well spent given the subsequent reduction in helicopter flying time. However, care should be taken not to over-pack nets Figure 5.65 A system of fixed and remote release either by volume (preventing the loops from being hooks can be used to maximise efficiency in the drawn together) or weight. field and thus reduce costs All strops should be attached to the nets prior to the arrival of the helicopter. Ground crews should be briefed and stationed at locations around the nets and at the drop zone (in case the release mechanism snags the strop). Commonly, nets or strops break, discharging the contents onto the bog so beware of this risk. Removing Chipped Timber The volume of material that can be packed into a net or sack can be increased by chipping on site prior to removal, hence reducing the number of helicopter journeys, although the resulting cost reduction may be outweighed by the extra cost of chipping (see 5.3.5.4). Also, the reduction in volume of material means that each sack or net is considerably heavier possibly requiring a larger helicopter at greater expense. The removal of the chippings is quite straightforward once a system of hooking and releasing the bags is devised. Large sacks used to transport animal feed or building materials are ideal for this purpose. The handles on the sacks should be reinforced and capable to withstand a full load of wood chips weighing approximately one tonne. These can be purchased from specialist sack manufacturers (in 1996, ÂŁ11 each). Some costs can be recouped through the sale of the wood chips for horticultural mulch or dressings for footpaths. Removing Whole Trees For mature plantations, the damage caused by standard tree removal methods can be reduced by whole tree harvesting and removal by helicopter (Brooks and Stoneman, 1996). To ensure the operation is as economic and effective as possible, effort should be made to minimise lost time through operational failures. The speed of the operation is dictated by the slowest component which is not necessarily the most expensive. Further research into plantation harvesting on peatlands is required before this method can be adequately assessed. 162


Conserving Bogs

5.3

Methods and techniques for Management

5.3.5.7 Removing Trees by Tractor and Winch Trees can be winched off the site without causing too much damage to the bog surface. As a small tractor or 4 x 4 vehicle is required to drive the winch, access to the site is a critical factor. The method is best suited to smaller sites or to removal of peripheral trees. At Muckle Moss, Northumberland, a team of four people removed 3ha of dense Scots pine and birch in five weeks. A Norse 5500 forestry winch was used to remove up to four medium sized trees per pull from distances in excess of 100m (Figure 5.66) 5.3.5.8 Specialist Extraction Machinery. Technology developed for Swedish forests has now been introduced to the UK in the form of the Vimek Minimaster 101. This is a low ground pressure tractor and powered trailer unit capable of extracting 2,000kg of timber per run. Initial tests have been favourable and it appears that this type of machine has potential for scrub and tree removal from wet peatland sites. Similar technology has been utilised in the forested peatlands of Switzerland for a number of years and has proved equally successful. For a full account of the Vimek Minimaster 101 in operation see Bacon and Lord (1996).

Figure 5.66 Using a winch to remove trees from the open bog

163


Conserving Bogs

5.4

Methods and techniques for Management

5.4 GRAZING Grazing of domestic and wild herbivores has had a significant influence on the historical development of peatland habitats (Thompson et al., 1995; Clarke et al., 1995; Welch, 1996) although the effect of grazing is difficult to separate from often associated burning and drainage. Indeed, the cessation of traditional grazing practices on raised bog nature reserves may be responsible for the increase in scrub and shrub communities (Ingram, 1996; Chambers, 1996); this is enhanced when sites are fenced-off also reducing natural grazing pressure. Re-establishing light grazing on raised bogs may have a positive effect on the vegetation by reducing shrubs and scrub and favouring Sphagnum communities. Grazing for conservation management may be used for:  control of scrub encroachment - new seedlings or re-growth from cut stumps;  control of ling heather - short-term strategy linked to hydrological management;  control of ling heather - long-term strategy where there is little potential to raise water-levels and;  maintenance of specific habitats created by grazing (for details see Rowell, 1988).

Overgrazing can lead to serious environmental problems (see 1.9/A1.3.3). In this section, some of the factors relating to changing or initiating grazing regimes are outlined, however, research and practical experimentation is still required. It is therefore recommended that any grazing initiatives are supplemented by detailed monitoring (see Part 4). Initiating new grazing regimes in order to fulfil conservation objections should be carefully considered before enacting. Factors to consider include: Foraging behaviour Several large herbivores are found on bogs. Most common are sheep, red deer, cattle, rabbits and mountain and brown hares. Each have differing preferences and requirements (see A1.3.3) producing differing vegetation communities in terms of composition and structure. Of these, most is known about the foraging behaviour of sheep, e.g. the MLURI hill grazing management model which can be used to set stocking rates on heather moor (Armstrong, 1993). Only certain breeds of sheep can cope with the poor grazing provided by bog vegetation. These include: Blackface, Swaledale, Welsh Mountain, Soay, Hebridean and Moorshnuke. The German Moorshnuke sheep have been used specifically for bog conservation objectives. Sheep have a narrow bite and preferentially select certain plant parts, e.g. growing buds and shoot tips. In contrast, cattle browse by wrapping their tongues around clumps of vegetation to pull them up. This results in an uneven vegetation structure and a comparatively larger amount of dead material is consumed. Thus, cattle may be used to restore old degenerate heather stands on drier heathland sites (Michael, 1992). However, only beef cattle can cope with the low nutrient status of bogs (see Rowell (1988) for relative grazing values of bog communities). Hardy breeds such as the Galloway or Highland are most appropriate. Pre-existing vegetation Bogs provide poor grazing and ditches can be dangerous for livestock. Digestibility varies according to the plant species and according to the time of year. The main edible species on bogs are ling heather, deer grass and purple moor grass. If heather is growing in discrete clumps, sheep will often eat the grasses and sedges growing between it rather than eating the heather itself. On species poor sites, cattle favour purple moor grass (often associated with past burning and overgrazing by sheep). Short term grazing programmes involving cattle or, cattle and sheep, can be utilised to control the initial development and subsequent spread of these species. Cattle may also select other species not particularly favoured by sheep such as mat grass and heath rush. Time of year 164


Conserving Bogs

5.4

Methods and techniques for Management

Different species become more or less palatable as the seasons change. In spring, cotton grasses provide an early 'bite', whilst purple moor grass is more palatable in summer. Heather is most palatable in the summer but may also be grazed in the winter when grasses become less available. As animals are likely to graze the most palatable plants, introducing grazing at different times of the year can be used to control different species. For example, to control birch scrub, grazing should be introduced in late spring when its leaves are most palatable. The time of year strongly influences the negative effects of grazing. Winter rains inevitably make bogs more susceptible to poaching. Poor winter grazing may only be maintained through supplementary feeding. If extra feed is used, a bog may suffer from eutrophication as animals defecate on the bog surface. Stocking levels Low stocking levels (e.g. less than 1 sheep per ha) allow sheep to graze selectively. In summer, more palatable grasses and sedges are grazed in preference to heather for example. In stocking levels are increased, vegetation types with a higher standing biomass, will be grazed earlier in the year even if they are less digestible than other available species. Thus, the stocking level can be adjusted to ensure control (via grazing) of certain species or groups of species. However, an increase in stocking density may lead to a complete loss of species through over-grazing, trampling damage and enrichment. There are few long term studies relating to grazing levels on wet bog (both blanket and raised) so guidelines for setting stocking levels are necessarily rather vague. Most studies concern grazing to maintain heather moorland (e.g. Armstrong and Milne, 1995; Armstrong, 1993; Gimmingham, 1992; Grant et al. ,1976; Grant et al. 1987; Hudson and Newborn, 1995; Rowell 1988; Welch, 1984; Yalden 1981). For example, one study sets stocking levels at less than 2.7 sheep h-1 a to maintain a healthy heather cover (Welch, 1984). However, on more waterlogged ground (bogs), stocking levels should reduced considerably (Welch, 1996). Welch and Rawes (1996), for example, found that a stocking level as low as 0.6 sheep ha-1 was checking heather growth on a north Pennine blanket bog. It is assumed that stocking levels set to maintain a healthy heather cover would be damaging to more sensitive communities and should be reduced accordingly (see Table 5.6). Table 5.6 suggests appropriate sheep stocking levels for conservation management based on a variety of studies. The suggested stocking levels should only be used as a rough guide. Local conditions, differing management objectives and the other factors outlined in this discussion must also be considered. A monitoring scheme should be implemented where grazing is introduced. Stocking levels should be reassessed on appraisal of the monitoring data. Table 5.6 Suggested Stocking Levels Habitat Dry Heath

Levels (sheep/ha) 1.5 - 3

Wet Heath

1 - 1.5

Degraded Bog

0.25 - 0.37

Wet Bog

<0.25

Comments Conservation management of dry heath though grazing usually focuses upon maintenance of heather stands. As for above. Other communities may become more important and sheep may have to be restricted to drier areas. As a means of controlling scrub and shrub invasion, light seasonal grazing may prove effective, either as a short or long term policy. Shepherding may be required. Large variability in habitat means that levels are difficult to assess. Light grazing may be beneficial. Natural grazing pressure may be adequate and can be altered with appropriate fencing.

Moderately heavy grazing regime (e.g. >2.5 sheep ha-1) reduces the cover of ericoid species hence promoting an increase in graminoids. Graminoids withstand defoliation better as they grow from the shoot base rather than the shoot tip (Welch, 1996). Reducing stocking levels also has an effect. An increase in cover and height of heather is a common outcome (Marrs and Welch, 1991). There may also be an increased build-up of dead woody material. Chapman and Rose (1991) reported a build-up of heather, cotton-grass, purple moor grass and wavy-hair grass litter following the cessation of light grazing at Coom Rigg Moss. This appeared to be responsible for a decline in both Sphagnum spp. and bog rosemary. 165


Conserving Bogs

5.5

Methods and techniques for Management

Supplementary feed Paradoxically, small amounts of supplementary feed increase the overall digestibility of sheep’s diet result in a greater forage consumption. Sufficient supplementary feed, on the otherhand, does reduce grazing. Grazing impact can thus be partly controlled by supplementary feeding. Accessibility The vegetation growing close to the preferred grazing area, for example, the edge of a bog, is more heavily grazed then that growing towards the centre of large patch of unpalatable vegetation. Burning Sheep prefer to graze newly burnt heather, possibly because of easy access, new grass growth and/or the higher nitrogen content of pioneer heather. Small patch burning (see 5.5) can help to spread grazing pressure across a peatland. Wetness Sheep do not like very wet ground and are likely to concentrate in drier areas. Cattle and red deer are particularly damaging on wet areas through poaching. Archaeology: Excessive poaching and enrichment may affect sub-surface archaeological remains (known or unknown) and can disturb the most recent part of the peat profile (see 1.6).

5.5 BURNING Upland landscapes which often include blanket bog (in Britain and Ireland) have traditionally been managed using fire (see A1.3.5). In particular, heather burning is used to create long (20-30m wide and hundreds of metres long) strips of different aged heather stands to create red grouse habitat. In these situations, the vegetation communities developed through careful and controlled burning - heather moorland (see Figure 5.67) in the main - are often considered to be desirable in nature conservation terms. However, these communities are not ‘naturally’ occurring bog communities so management objectives should be clearly defined before considering the use of fire (see 3.2). For bog conservation, burning is rarely used. There may be a temptation to control heather or scrub on bogs by burning. However, without hydrological management, burning is likely to stimulate heather and scrub re-growth; burning to control heather and scrub is unsustainable. As a general rule when conserving bogs - if in doubt, do not burn. The following principles are taken from the Manual of Grouse and Moorland Management (Hudson & Newborn, 1995) which should be consulted for more detailed information:  Burning removes degenerate heather, dead woody material and litter, stimulating growth of the stand. It provides a patchwork of uneven aged heather, utilised for breeding, nesting and feeding of red grouse (Lagopus lagopus).  Following fire, the principle regeneration method of young stands is from the root stock, whereas old stands regenerate better from seed. For 12 year old heather, 58% of stems regenerate where only 10% regenerate from 25 year old stands. o  Seeds germinate after exposure to heat (40 - 100 C) for less than one minute.  As little as 30% of vegetation is burnt in a cool fire and 90% in a hot fire.

166


Conserving Bogs

Methods and techniques for Management

5.5

Figure 5.67 Patchwork of burnt and unburnt moorland There are numerous problems associated with burning on a regular basis although most of these can be overcome by following the guidelines laid down in The Muirburn Code (SNH, 1994) and The Manual of Grouse and Moorland Management, Chapter 2, (Hudson and Newborn, 1995). They both stress the need for a rigorous burning plan and its careful implementation with regard to the variety of habitat, aspect, season and adjacent land use. Statutory regulations (Hill farming Act, 1946; Wildlife and Countryside Act, 1981; Wildlife and Countryside Act (Amendment) 1985; Highways Act, 1980; Clean Air Act, 1956 and Health & Safety at Work Act, 1974) governing burning on peatlands (refers to UK. only) are:  Heather burning is only allowed between 1 October and 15 April (30 March in lowland areas).  Burning between 1 October and 30 April is allowed on the authority of a proprietor or of the relevant Agricultural Department (SOAFD, MAFF, WOAD) above 450m (1,500 feet), extendible with permission to 15 May.  Tenants must give landlords 28 days written notice.  Notify neighbours with 24 hours written notice of the date, place and intended burning area.  Burn only at night between 1 hour after sunset and 1 hour before sunrise.  Never leave a fire unattended - you must ensure all fires are out.  Never let the fire get out of control or at least satisfy authorities that all reasonable steps were taken for its proper control.  Do not damage woodland or neighbouring property with fire.  Always keep to the stated prescriptions of heather burning on a Site of Special Scientific Interest.

These regulations apply to the burning of all types of moorland vegetation and not just heather. Contravention of these regulations may, on conviction, entail a fine of up to £1,000, or £2,500 if appropriate procedures are not adopted on a SSSI (SNH, 1994).

167


Conserving Bogs

5.6

Methods and techniques for Management

5.6 ACCESS PROVISION 5.6.1 Introduction Peatlands are susceptible to damage from both pedestrian and vehicular traffic (Slater & Agnew, 1977; Habron, 1994); the most severe impacts relate to heavy and localised traffic over wet, Sphagnum dominated, bog (Emanuelsson, 1985). Dry, often degraded, bogs have a greater carrying capacity due to more resistant woody shrub vegetation and a firmer surface yet are still sensitive to repeated trampling by vehicular traffic. Provision of access facilities is usually designed to restrict surface damage although the access provision itself may have an influence on vegetation or on the physical properties of the peat. Larger, more permanent, structures have more effect. As a rule, it is better not to over-cater, taking a minimum approach and modifying as necessary. The type of access provision is also determined by its intended use. For public access and special needs requirements, safety and finish should always be considered. Access for management does not require the same level of sophistication but may have different demands. This section outlines the different types of access provision commonly used on bogs. Table 5.7 suggests appropriate provision according to the type of use and its characteristics. Table 5.7 Access Provision Hydrological Characteristics (uncut or cutover bogs) Wet: water levels at or close to the surface; pool systems.

Seasonal or spatial variations; wet and dry areas.

Dry - water levels low - seasonally wet.

Botanical Characteristics

Dominated by Sphagnum and other wet bryophyte communities or bare peat.

Broad species mix; wet Sphagnum dominated areas and dry shrub zones.

Dominated by dwarf shrub and scrub species.

Peat Characteristics

High water content; Sphagnum peat.

Variable

Dry and compacted with continuous vegetation cover.

Timescale

Traffic Pressure and Ensuing Damage

Pedestrian Access Provision

Low Ground Pressure Vehicle Provision

Permanent

Serious damage can result from even light use.

Raised Boardwalk (5.6.2) Floating Boardwalk (5.6.3)

Permanent road or track (5.6.5); re-route where possible.

Temporary

The wettest and most heavily used areas are most prone to damage.

Sections of boardwalk over wet areas (5.6.6)

Floating track sections. (5.6.3)

Permanent

Localised damage; dry zones may sustain moderate use.

Sections of boardwalk over wet areas (5.6.6). If heavy use is predicted a permanent boardwalk may be required.

Re-route around wet areas.

Temporary

Temporary use for management or monitoring access

Temporary paths (5.6.4) or boardwalk sections (5.6.6).

Temporary tracks (5.6.4)

Permanent

Permanent use damage to vegetation may lead to exposure of surface and erosion.

Permanent paths -terram matting/woodchip (5.6.5)

Temporary tracks (5.6.4)

Temporary

The surface should withstand light or temporary traffic.

No provision required.

No provision required.

168


Conserving Bogs: The Management Handbook

5.6

Part 5: Methods and Techniques for Management

5.6.2 Raised Boardwalks 5.6.2.1 Introduction The most common and effective way of encouraging visitors on to wet bogs is to use a boardwalk. They fulfil two main functions: to protect the bog surface from the damaging effects of regular or heavy pedestrian trampling (see 1.12/A1.6.5) and to protect the pedestrian from the difficult wet terrain of the bog. The boardwalk also serves to encourage visitors to stay on the route of the boardwalk and not walk over dangerous and/or sensitive areas of bog (Figure 5.68). Figure 5.68 A boardwalk at Askham Bog, Yorkshire (Kirsten Smith) 5.6.2.2 Materials Boardwalks have been successfully constructed from both treated and untreated timber. It is essential that treated timber is left to 'weather' before installation so any excess chemicals are leached out before they can damage the bog. There have been one or two cases reported where treated timber has leached chemicals into the surrounding peat and killed off the vegetation. There is not enough published information to give firm recommendations for specific chemicals, treatment processes and weathering times. There are advantages in using treated timber: its increased life expectancy, its price and general availability. However, until further information emerges, it is recommended that treated timber is used with great care. Untreated hardwoods may be more appropriate; suggested British hardwoods for maximum durability are oak and chestnut. Elm is also commonly used but its availability is now quite restricted in the UK. For more information on qualities and suitability of different wood, see Agate (1983). Pre-formed recycled plastic can be used as an alternative material to wood. Plastic â&#x20AC;&#x2DC;woodâ&#x20AC;&#x2122; is hard wearing, non-corrosive, non-toxic, non-slip, it requires no pre-treatment, and has the 'appearance' of timber. Its durability and low-maintenance requirement make it ideal for wetland boardwalks although, as yet, it has had limited application on peatlands. Initial costs may be slightly higher than for hardwoods although these should be recouped in lower maintenance and replacement costs. There should also be scope to mix the two materials in the same construction, perhaps by installing wooden decking over plastic stobs. 5.6.2.3 Construction Where possible, the boardwalk should avoid wet areas or those areas that are particularly sensitive to visitor pressure, i.e. bird nesting sites. Also, avoid constructing in non-aesthetic, long, straight lines. Provision should be made to protect the bog during installation; this may require temporary paths (see 5.6.4) over particularly sensitive areas, site entry and exit points. Raised boardwalks provide an excellent opportunity to increase accessibility to the countryside for those people with special needs. If this is intended, consultation with local special needs groups prior to construction is recommended. Boardwalk dimensions depend largely on the intended use. For heavy use, a width of at least 900mm should be used and for one-way, occasional, use about 750mm. Different dimensions are required for disabled access. Passing places and information points may require wider sections. Detailed boardwalk specifications can be found in Agate (1983) and CCS (1989). Most raised boardwalk designs work on the principle of horizontal decking attached in sections to vertical stobs (Figure 5.69). Care should be taken to minimise slippery surfaces - rough wood decking or wire coating can be used to reduce this hazard (Agate, 1983).

169


Conserving Bogs: The Management Handbook

Part 5: Methods and Techniques for Management

5.6

It is important on peatland sites to make sure stobs are sufficiently large to stop sinking in waterlogged conditions. Stobs should be sunk at least 750mm below the surface level and have a minimum surface area of 100mm2. The vertical stob is prone to rotting at the peat/air/water interface so special attention should be given to the durability of materials at that point. Areas of mature scrub are problematic as roots make it difficult to insert the vertical stops into the peat.

Figure 5.69 A typical raised boardwalk design. The length of vertical stob below the surface is dependent on the nature of the peat

When working in particularly soft peat, do not cut a point on the stob ends. A flat end provides a firmer support for the boardwalk and prevents sinking.

5.6.3 Floating Boardwalk 5.6.3.1 Introduction An alternative to raised boardwalks (see 5.6.2) are simpler 'floating' boardwalks which are suited to flatter, drier situations. Heavy wooden blocks or logs sit directly on the bog surface and support various designs of top planks or decking (Figure 5.70). 5.6.3.2 Materials Railway sleepers have been used extensively for floating boardwalks either longitudinally or in horizontal section (Figure 5.70). They are easy to work with as they are of uniform shape and size, have excellent durability and provide safe strong support. Availability and prices are variable throughout the country. Rough sawn wood may provide an alternative to sleepers if they are either too expensive or not available. However, when using wood derived from the site problems may be encountered in obtaining enough material of even proportions. The durability and finish may also be inappropriate. 5.6.3.3 Construction Principles There are various designs currently employed for floating boardwalks although they all tend to follow basic principles. ď&#x201A;ˇ Ground supports should be spaced along the length of the boardwalk spreading the weight of surface decking and people. Place ground supports on drier ridges to span the boardwalk over wet hollows. Sleepers can be placed either longitudinally or in horizontal Figure 5.70 If available, an effective and durable boardwalk can be made from railway sleepers section. ď&#x201A;ˇ The top decking can be constructed from sleepers (lain longitudinally) or sawn timber. ď&#x201A;ˇ Sleepers can be placed horizontally directly over the ground (with no support), in which case the vegetation immediately underneath the boardwalk may die and the decking may consequently sink. If such horizontal decking is used, wire should be stapled across sections to deter vandalism or movement.

170


Conserving Bogs: The Management Handbook

5.6

Part 5: Methods and Techniques for Management

 If the surface becomes slippery when wet, chicken wire or similar can be stapled on for better grip.

5.6.4 Temporary Paths 5.6.4.1 Introduction There may be situations where sections of bog are intensively used over short periods of time such as:  during management operations especially at site entry and exit points; and,  during low intensity monitoring of fixed installations, again including entrances and exits where pedestrian pressure is greatest.

In these situations, a solid construction boardwalk is unnecessary; temporary paths can be built instead. 5.6.4.2 Brash Paths As a bi-product of scrub clearance, whole saplings and brashings can be laid over wet or bare peat areas. The brashings should be well packed down with larger material at the base and finer brashings at the surface. This protects the surface from irreparable damage although it may cause localised enrichment as the wood rots. Brash can either be taken back up, or left as a semi permanent path (topped up when necessary). 5.6.4.3 Plastic mesh Polythene and polypropylene mesh (often termed geogrids) can be used as either a temporary surface path or a permanent footpath base (see 5.6.5). Choose a material that is light (easy to transport), UV stable, acid resistant and non-toxic to plants. Mesh sizes in the range of 20-35mm are most suited to peatland sites. If the mesh is left on the ground, holes should be large enough to allow plants to grow through, hence binding the mesh to the surface and increasing the path's durability. It is also necessary to fix the mesh in place with stakes or by digging it into the peat along the length of both sides. If the path is infrequently used, the mesh can be rolled up and taken off site. 5.6.4.4 Inflatable Path Developed for the emergency services to be used over ice, mud, shallow water or unstable ground, the inflatable path is made from rot and chemical resistant Alcryn coated nylon. Its use has never been tested on peatlands although in situations where access is needed to seasonally inundated monitoring equipment or where areas of very unstable peat need to be crossed, this portable (packs down to 787x533x406mm) platform may be useful. 5.6.4.5 Plastic Path A cheaper alternative to an inflatable path is a plastic path - Portapath. This is a lightweight sectioned plastic path manufactured for use in the garden. It comes in 3m and 6m lengths and can be joined either lengthways or sideways. The Portapath costs £20 for 3m and is available from garden or horticultural suppliers.

5.6.5 Permanent Footpaths 5.6.5.1 Introduction Sites that experience heavy pedestrian pressure may require permanent access provision; either as a boardwalk (see 5.6.2) over wet, deep peat or a footpath over more durable terrain (i.e. cut over bogs or thin blanket peat). A permanent footpath deters the formation of casual walkways (desire lines) and reducing erosion and trampling associated with peoples avoidance of eroded wet patches. A wide variety of materials and methods are discussed in Agate (1983) and it is recommended that this volume is used as a reference before deciding on, or implementing, any footpath work.

171


Conserving Bogs: The Management Handbook

5.6

Part 5: Methods and Techniques for Management

5.6.5.2 Materials The materials used depend upon the site characteristics. Deep peat requires a firm sub-base to support a top dressing such as geotextile and woodchips whilst thinner peat may already lie over a firm mineral base that can support stone blocks. Materials used include: 

Geogrid/textile and stone: Geogrids are specially engineered plastic meshes. They form an effective base beneath stone on peatland sites. This type of path is best used on degraded sites where pedestrian traffic is particularly heavy.

 Geotextile and woodchips: Geotextile materials (e.g. Autoway 120) are designed to act as a reinforcing base. Woodchips can be derived on-site from scrub clearance operations or purchased from timber merchants.  Stone: Where locally available, large stones can be used to reinforce footpath sections on thin blanket peat. If they are used on deep peat sites they may sink. On deep blanket peats in the Cheviots, the Pennine Way has been strengthened successfully by using large flat paving slabs taken from disused Lancashire cotton mills. These slabs are very heavy (they have to brought in by helicopter) and yet, remarkably, float on the peat.  Log sections or chestnut palings: Laid directly onto wet peat, wooden pathways tend to sink as their movement stirs up the supporting peat into a soupy mess. On drier peats, on thin blanket peat or over a suitable sub-base, these pathways may offer a durable surface and provide a suitable use for waste derived from scrub and tree clearances. Over areas of deep peat, log sections can be hammered in vertically.

5.6.5.3 Construction Geogrid and Stone  All scrub and large shrubs should be removed from the line of the path.  Dig a tray (a shallow flat trench) to a minimum depth of 18cm below the surface. Cut the geogrid to the desired width and lay it in the base of the tray. Pegs should not be required as the weight of the stone should keep it in place.  Cover to a depth of about 16cm with a layer of aggregate (type one or equivalent). This should be adequately compacted before a final 1-2cm of fines is added as a surface dressing.  To avoid enrichment, limestone or other alkaline rocks should not be used for such construction.

Geotextile and Woodchip  Clear the intended route of obstacles such as roots and stones and create a level surface. Bushy vegetation should be flattened down (or cut) but not removed. Wet hollows are best avoided.  Lay the geotextile in long lengths (>20m at a time), digging the edges down into the peat. These can be staked if necessary. It is important that the material sits as flat to the surface as possible. On very dry sites, it may be possible to scour the surface and remove any obtrusive vegetation.  Face the geotextile with a good coating of woodchips, approximately 12-15cm depth. These settle over time and become compacted so an annual top-up is usually necessary (Figure 5.71).

Decomposition of the woodchips may enrich areas at the edge of the path.

Stone Paths  Test the depth of peat along the required route; it should be no deeper than the vertical axis of the stone blocks.  Hammer the block into the peat with a heavy rubber mallet (paviour). The stone should sit with its flattest face upwards, to provide a reasonably smooth walking surface. It should also be wide enough at the base to prevent the stone toppling over.  Space the stones along the path to act as 'stepping-stones', rather than packing them closely together. If the stones are able to move around freely in the peat it quickly loses its structure.  If the stones do not rest on the substrate comfortably, larger flat slabs can be placed on the bog surface. This is only appropriate on very heavily used sections of firm peat (Figure 5.72).

172


Conserving Bogs: The Management Handbook

Part 5: Methods and Techniques for Management

5.6

Figure 5.71 Paths can be underlain by a membrane of geotextile or geogrid. They can be surfaced with stone or wood chips, depending on pedestrian 5.6.6 Short, Temporary Boardwalks These are used mainly for protection of monitoring installations and entry/exit points during management operations. Duckboarding and ladders are often used. Duckboards are usually narrow (approximately 50cm), short (approximately 1m) lengths of boardwalk decking attached to two lateral stringers (Figure 5.73). They are portable, cheap and easy to construct making them ideal for temporary access provision. Where access over difficult or wet terrain is required (for example, during dam construction) or protection around monitoring installations is necessary, duckboarding can protect the surface well. Duckboards can be constructed from any material, as long as it is reasonably hard wearing and does not leach any harmful chemicals into the bog. Wooden pallets can also be used. Aluminium ladder sections are a good alternative to wooden duckboards. They are very light, strong and non-corrosive. They can be purchased for about ÂŁ15 (1996).

Figure 5.72 With care, large stones can be used to provide durable pedestrian access over deep and shallow peat. Figure 5.73 A basic design for a wooden duckboard. As a lighter and more durable alternative, aluminium ladder sections can be used.

5.6.7 Permanent Roads and Tracks 5.6.7.1 Introduction Permanent vehicle routes across bogs should not be established as it is better to re-route around the bog to avoid serious hydrological and botanical damage. However, if there are no alternative routes, there are some options to alleviate erosion. Note, uncontrolled use of low ground pressure (LGP) vehicles (see 1.12) over wet peat can cause extensive damage (Figure 5.74).

173


Conserving Bogs: The Management Handbook

5.6

Part 5: Methods and Techniques for Management

Where vehicle damage is limited to small areas of wet ground or is seasonal in nature, temporary short sections of track or surface reinforcement may be adequate, otherwise permanent tracks have to be constructed. These specialised operations should be planned by engineers. The problems associated with building over deep peat are considerable. Subsidence, fluctuating water levels, wash outs, cracking and structural loss may all cause road failure. Further, it is important to take into account archaeological considerations. Any major track or road construction, especially across peatland, should be assessed and evaluated with respect to archaeology. Regular maintenance may be necessary and provision should be made. Potentially nonaesthetic linear features also detract from the visual appeal of open landscapes. If the peat is thin it is advisable to excavate to the mineral substrate. This provides a better foundation for the track although it modifies the hydrological character of a peat body (Figure 5.75). Flow characteristics above and below a newly constructed road are modified possibly resulting in erosion by channelisation, or cause the drying of the adjacent peat. Imported material or exposure of the mineral substrate may also serve to change the chemical composition of the water flowing through the peat resulting in local eutrophication and vegetation change.

Figure 5.74 Damage caused by vehicles or pedestrians can quickly spread laterally if it is not contained and managed properly. 5.6.7.2 Materials Construction materials for deep peats often have to be imported from elsewhere making access to main roads important. Upland sites offer better opportunities to use locally derived materials, than lowland bogs, reducing construction costs and possibly helping to reduce the visual impact on the landscape. The

174


Conserving Bogs: The Management Handbook

Part 5: Methods and Techniques for Management

5.6

Figure 5.75 Hydrological flow characteristics of water through blanket bog - before and after road construction substrate and surface materials required ultimately depend on the types of vehicles which are likely to use the track (their ground pressure, tyres and the frequency of their intended use). 5.6.7.3 Construction The two main techniques currently employed are: ď&#x201A;ˇ The floating road or 'on-top construction' (Rowan, 1976) favoured by the Forestry Commission over deep peat sites. ď&#x201A;ˇ The solid substrate road which sits directly on the underlying mineral ground usually in thin peat areas.

One of the main problems associated with a floating road is the tendency for it to sink under its own weight. This is partially countered by the use of a brash and log substrate in the Morris design (Morris, 1990). The use of an artificial mesh, such as terram, laid underneath the brash or directly underneath the aggregate 175


Conserving Bogs: The Management Handbook

5.6

Part 5: Methods and Techniques for Management

infill may also serve to deter sinking. Note that wood should be laid below the water table to prevent decomposition. Provision must be made for road drainage, either by construction of a camber, cross fall or by underground culverts. This helps to prevent both the washing away of surface material and the loss of cohesion within the substrate infill (through saturation). Whatever method is employed, annual maintenance is usually necessary. Re-surfacing and drain clearance are the most common.

5.6.8 Temporary Vehicle Tracks Where possible, always re-route around wet, sensitive areas onto firmer terrain. If this is not possible and there are no alternatives to using vehicles, then the use of temporary protection or short sections of permanent reinforcement may be necessary. Hinged hardwood boards laid as a double row offer excellent short-term protection from vehicle damage. The boards consist of approximately 20 hardwood strips joined by two transverse steel bars, looped at the end to allow fixing to consecutive boards. Boards can be purchased or hired. Temporary reinforcement by heavy duty plastic netting laid directly onto the surface may provide adequate protection from the shearing motion of ATV tyres. Plastic netting is particularly useful during management operations where people and materials need to be transported across difficult or wet terrain. The use of a vehicle and surface protection may cause less damage than unprotected pedestrian access (and may be cheaper by cutting labour costs). 5.6.9 Vehicles Vehicle use over a wet peatland surface should be avoided as extensive long term damage results even through infrequent use. If vehicle use is envisaged, it is important to use a vehicle with low ground pressure tracks or tyres and to follow routes which avoid the following: wet areas, steep inclines, Sphagnum lawns, pool systems or flushes. Firmer ground such as thin peats, mineral outcrops (on blanket bog) and areas dominated by less sensitive vegetation (dwarf shrub and scrub communities) should be used for vehicles if absolutely necessary. If damage occurs then construct temporary or permanent trackways (see 5.6.8, 5.6.7). Wide tracked excavators either working on mats or directly on the surface have been utilised extensively on the Solway mosses with little damage to the bog surface. Access problems are particularly acute on very large rehabilitation sites. In these situations, a small hovercraft could even be considered. There are two main vehicle uses on peatlands: ď&#x201A;ˇ Transportation of people: Small ATVs such as quad bikes can be used for the transport of 1-2 people. On large areas of blanket bog these machines have proved particularly useful. They are also useful on large degraded raised bogs (raised baulks in particular offer good, firm access). The transportation of more people requires a vehicle such as an Argocat. This vehicle, fitted with 6-8 balloon tyres, can transport up to six people without causing too much damage. ď&#x201A;ˇ Use for Management Work: Materials for management work can be transported by hand (labour intensive and impractical on large sites) or by helicopter (very expensive). An alternative is to use vehicles such as Glencoes which have successfully been used on many peatland sites. More recently, timber extraction on bogs has been made more cost effective by the use of specialised equipment such as the Vimek Minimaster 101 (see 5.3.5.8). Most of the large engineering jobs, such as the construction of bunds and dams requires the use of an excavator. Many of the manufacturers produce excavators with wide tracks which, with care, are capable of working safely and effectively on deep peat.

176


Conserving Bogs

YPP Survey and Monitoring Specifications

APPENDIX 1 SITE ASSESSMENT OF BOGS FROM THE DAMAGE SUSTAINED A1.1 Introduction A1.2 Peat Extraction A1.3 Agriculture A1.4 Commercial Afforestation A1.5 Development A1.6 Other Forms of Damaging Activities A1.7 Indirect Forms of Damage

177


Conserving Bogs

A1.1

YPP Survey and Monitoring Specifications

A.1.1. INTRODUCTION Before the agricultural revolution in the eighteenth century, bogs were held in high regard according to many writers of the time (Smout, 1996). They were valued mainly as a source of fuel but also as providers of winter hay and as ground to provide sheep and cattle with an early â&#x20AC;&#x2DC;biteâ&#x20AC;&#x2122; in spring. Attitudes changed in the nineteenth century as agricultural improvers saw the land as capable of betterment. From this time, until very recently (last 10-20 years), peatlands were primarily considered as unproductive land. This resulted in dramatic changes in landuse on peatlands throughout Europe. Such changes have resulted in widespread damage to peatland ecosystems. This appendix (summarised in Sections 1.8-1.14) describes the types of uses bogs have been subjected to and the resulting damage they are likely to have sustained. It then goes on to describe the ecological effects and how they can be recognised. This section can thus be used to assess the characteristics of a site in terms of the damage sustained. This helps to construct a useful site description (see Part 3) and also sets the basis for setting realistic management objectives and prescriptions for achieving those objectives. The appendix is divided into the following sections:

A1.2. PEAT EXTRACTION A1.2.1. INTRODUCTION Peatlands, often regarded as wastelands in agricultural terms, have long been used as a mineral resource. Peat is high in organic matter (nearly 100%), light, has excellent water retention properties and is easy to cut. Peat has probably been used as fuel for many thousands of years and many peat bogs show signs of a long history of domestic peat cutting. More recently, the properties of peat have been exploited by the horticultural industry. For the bog conservation manager, the effects of peat extraction (whether recent or ancient) are often one of the main causes of bog degradation. In this section, the types of peat cutting and their effects are considered. Over the years peat production/extraction techniques have developed and adapted to accommodate changes in the market. Peat extraction via hand-cut domestic peat banks have been superseded by large commercially run operations which mill peat into piles across a bare surface. Central Ireland provides a spectacular example of this change where the Great Bog of Allen has been turned into a seemingly black and featureless desert (see Figure 1.12). Peat use is dictated by the properties of the peat itself which vary according to site characteristics and bog type. Fuel peat is derived from both blanket (mainly) and raised bogs whilst peat for the horticultural industry tends to emanate mainly from raised bogs. However, whatever type of bog is used, or techniques employed, there are several common features: drainage, provision of access routes, removal of surface vegetation and drying of cut peat on the surface (Wheeler & Shaw, 1995). Hand cutting of peat for domestic fuel has been a traditional and widespread method of extraction resulting in extensive areas of cutover blanket and raised bog. This traditional activity has declined as communications have improved and other fuel types have become more widely available. However, active domestic peat cuts are still a feature of many parts of rural Scotland and Ireland. In some areas, traditional hand-cutting has been replaced by modern techniques such as sausage extraction. Small-scale co-operative ventures by people owning adjacent peat banks have accelerated this process and in some cases, a cottage industry of semi-commercial, small-scale ventures has been established. Other uses for peat include animal bedding (moss litter), whisky production, fuel for power stations and production of charcoal briquettes for barbecues. More recently, peat extracted from raised bogs has been used as a growing medium and soil conditioner for the horticultural and amateur gardening industries. Varying uses require different extraction techniques to result in differing degrees of damage. The extraction technique then influences the types of after-use an exploited area can be used for, and its potential for rehabilitation towards a bog habitat.

178


Conserving Bogs

A1.2

YPP Survey and Monitoring Specifications

A1.2.2. GENERAL EFFECTS OF EXCTRACTION Many of the effects of peat cutting are common to different extraction techniques. This is partly the result of similar methods required to prepare a site for extraction, e.g. drainage and vegetation removal. Common features are detailed below: Drainage (see A1.3.2) Resulting in drying, compaction, oxidation, wastage and a changed water-table response pattern to rain events. In effect, an uncharacteristically highly fluctuating water level pattern is produced which is unsuitable for many bog plants such as Sphagnum spp. Enrichment can be caused by three inter-related effects of peat cutting:  Peat cutting may expose underlying rich fen peat (more likely on former raised bogs), the mineral substrate or ground water leaving the resulting surface relatively richer in nutrients (see Figure 5.49).  Extensive removal of peat may change the local hydrology of an area considerably. For example, a formerly water shedding dome may be converted into a water collecting basin following extensive removal of peat. Water from surrounding land is likely to be of a higher nutrient status than ombrotrophic bog water.  Drainage and exposure of bare peat surfaces may mobilise nutrients sufficiently to affect the vegetation. The exact nature of this release and utilisation needs further investigation (Wheeler & Shaw, 1995).

Loss of stratigraphic record either entirely or at least in part. The following effects are common to only some of the extraction techniques: Steep hydrological gradients: Block (sod) and domestic peat cutting often give rise to unnaturally steep hydrological gradients at an unnaturally abrupt edge to the peat body. On raised bogs, this changes the 'ground water mound' (see 2.5) of the whole peat body though the main effects are confined to the edge of the bog where lowered water levels should be apparent. Peat cutting within the peat body may also result in an uneven land surface. Raised blocks act in a similar way to an individual 'raised bog'. Within each block of peat, water-levels fall to an equilibrium based upon the block’s ground water mound. As a result, the surface of the bog becomes drier. Resultant atypical vegetation establishment may then exacerbate the drying effect (Wheeler & Shaw, 1995). Extensive bare peat surfaces: Exposed dark peat surfaces absorb more heat than a vegetated surface causing increased water loss and higher levels of microbial activity. Bare peat areas are also susceptible to wind and water erosion. Blanket peats forming in cool and wet climates, often on sloping ground, are particularly vulnerable. Additionally, high temperature and water level fluctuations coupled to a generally smooth surface topography of bare peat surfaces makes plant colonisation difficult. Commercial extraction operations often camber the peat fields for enhanced drainage. As a result, water collection areas are rare hindering recolonisation by bog vegetation.

A1.2.3. DOMESTIC EXTRACTION Peat cutting for use as a domestic fuel (Figure 1.10) is a traditional rural activity which is still carried out in many parts of Europe. Even though peat cutting by hand methods can be labour intensive and hard work, it is still pursued by in many localities where there is a strong cultural connection to the use of peat. This is despite the advent of mechanical methods for peat extraction such as the DIFCO cutter which can be operated using a farm tractor. The techniques employed require the use of special peat spades which are characteristically flat rather than curved (Figure 5.13). The surface vegetation is removed and laid to one side. Peat below this layer is then cut out in blocks and laid on the vegetated surface to dry. On raised bogs, peat cutters may discard the upper less humified ('white') peats and dig deep faces to extract the darker more humified 'black' peat which is more suitable for burning. Gradually, the peat face moves forward and vegetation is relaid on the bare peat surface exposed behind the bank. Extraction is fairly slow allowing recolonisation to keep up with the 179


Conserving Bogs

A1.2

YPP Survey and Monitoring Specifications

forward extraction of the bank. On blanket bogs, worked faces are generally orientated down the slope to facilitate drainage so that little or no artificial drainage is required. The effect of peripheral peat cutting on raised peatland has probably been seriously underestimated in the past. The position of the water table in raised peatland is governed in part by the shape and depth of the peat deposit and in part by the hydraulic properties of the peat. The height of the groundwater mound is poised in equilibrium. This idea, proposed first by Ingram (1982), suggests that changes to the shape of a deposit, for example by a reduction in the basal area by domestic peat cutting, influences the equilibrium height of the groundwater mound. The expected trend based on model predictions is for the water table to fall below the original equilibrium height until a new equilibrium establishes. The rate at which the groundwater mound readjusts to the new height can only be left to conjecture. It is suggested that oxidation of peat on its own limits readjustment to a few centimetres per year. Compression of peat, collapse and subsidence could assist the process further, though in many cases this may be insufficient to prevent changes in the typical flora from occurring (for example, from bog to heath). Some of the drying effects may be moderated in areas of higher rainfall. For example, domestic cutting around Raheenmore (Ireland) seems to have caused a progressive loss of pool communities within the last 30 years (Ryan, personal communication). Cutover areas may support a variety of vegetation types dependent on the severity of the cutting. An often uneven surface is characteristic supporting a variety of 'acid' vegetation communities ranging from heath, in drier areas, through to bog pools. If extraction has been sufficient to reach underlying fen peats, mineral deposits or ground-water, then a fen community is likely to develop. The ecohydrological effects of domestic peat cutting on blanket bog may be less severe. Blanket bogs (more accurately blanket mire - see 2.3.2) are more diverse than raised bogs composed of a variety of differing vegetation assemblages. The practise of relaying vegetated turfs on bare peat behind the peat bank facilitates rapid recolonisation. However, eventually an unnaturally uneven surface results, leading to a mosaic of wetter (cut-away areas) and drier (remaining uncut baulks) areas. Where cutting has ceased, recognition depends on the following factors:  Time since abandonment. Very old peat faces may be masked by recolonised vegetation. Shrinkage, cracking and wastage of peat allied to slumping gradually reduces the height of the peat bank.  Type of vegetation established after cutting. Certain vegetation assemblages such as fen, fen carr and trees (both selfsown and planted) may mask cutting activities.  Extent of cutting. Extensively cut areas may be difficult to recognise if a wide area has been cut away to leave flat surfaces. Careful examination, however, usually reveals the remains of peat cuts or baulks. A useful tool to identify such cutover sites is stereo air photography which often reveals straight or slightly curved lines of old peat cutting banks. 3-D stereo image will also reveal hitherto hidden small height differences, often arranged in a regular pattern, across the surface of the peat bog.

A1.2.4. PEAT EXTRACTION BY EXTRUSION – SAUSAGE CUTTING Traditional hand cutting of peat is now being gradually replaced by sausage extraction (Figure 1.14). This extraction technique uses a machine to drive over a peat bog to cut a series of angled slits at a depth of about 1m. Peat is then extruded, from the base of the slit to the surface, as a long ‘sausage’ which is divided into lengths of 20-30cm and left on the surface to dry. Dried peat 'sausages' are typically used for domestic fuel and also in the whisky industry. In the past, it was common to dry 'sausages' on vegetated surfaces. However, problems relating to the peat ‘sausage’ becoming entangled with vegetation during mechanical removal has meant that commercial operators now strip surface vegetation away. Where peat is dried on a vegetated surface, the combined actions of driving machinery across the bog surface and the physical presence of drying peat alters vegetation communities and may lead to extensive areas of bare peat. Significant damage to surface vegetation has been recorded after only one harvest; further changes result from continued cutting (Meharg et al. 1992). Before extraction, peripheral and/or widely spaced drains are cut in order to drain the bog sufficiently to allow the passage of heavy machinery. Drainage is assisted by sub-surface slits which act as 'mole' drains. 180


Conserving Bogs

A1.2

YPP Survey and Monitoring Specifications

Note that the slits usually seal at the surface but may well be open below ground. Commercial extractors also camber extraction fields to improve surface water runoff although this is difficult to discern in the field. Drainage, vegetation removal, repeated travel across the bog surface by machinery, large amounts of peat lying on the bog surface and sub-surface drainage channels all serve to badly damage the bog. The peat archive is disturbed and gradually destroyed whilst intense physical disruption of the peat structure may even result in peat liquefaction preventing further cutting and hindering vegetation colonisation. Active sausage cut sites are easy to discern by the presence of peat sausages (thin cylinders 20-30cm long by approximately 10cm in diameter) left on the surface to dry. Extrusion slits are less obvious where they have sealed at the surface given that they are usually cut at an angle. Slits become more obvious in dry weather as the surface cracks along slit lines. After abandonment, vegetation recolonisation of bare peat surfaces is slow. Initially, a species poor vegetation assemblage of sedges and the mat forming mosses form. Hareâ&#x20AC;&#x2122;s tail cotton grass is particularly common. Soft rush colonisation indicates extensive removal of peat and an increasing influence of ground water.

A1.2.5. BAULK AND HOLLOW/BLOCK (SOD) CUTTING A major historical use of peat was as moss litter for livestock bedding. Moss litter was usually extracted from bogs with poorly humified peat (raised bogs in the main). Originally, peat was cut by hand - a highly labour intensive industry. After sufficient drying, peat was milled or shredded to produce a bulky, highly absorbent and odourless material for animal bedding. As the litter industry declined, block cutting of peat was used to supply a burgeoning horticultural demand. From the 1960s, block cutting by hand was replaced by mechanical cutters although the same pattern of baulks and hollows (Figure 1.15) was still produced. Before the late 1960s, most operations were carried out by hand. Bogs were cut in a regular pattern of baulks (low ridges) and cut out hollows or peat fields. Sites were drained by a regular network of drains. More recently, commercial operations have switched away from block cutting to milling. The resulting block cut pattern leaves a very unnatural surface. Cutting fields or hollows may stay reasonably wet depending upon drainage characteristics. Upstanding baulks do, however, dry considerably as a result of steep hydrological gradients between baulks and hollows. Baulks are usually too dry for Sphagnum recolonisation. Repeated passage of machinery across cutting fields compacts peat further altering its hydrological properties. Once extraction activities cease, drier areas such as the baulks are prone to colonisation by scrub, notably birch, or dry heath vegetation. Hollows tend to be wetter and may even flood as drains infill. The extraction system results in a distinctive pattern of baulks (raised ridges) and hollows (areas from which peat has been removed). The resultant pattern consists of a series of parallel and rectangular channels, of similar length and width (length is variable, but width is generally 2-3m) cut to a depth of 1-2m. Each cutting field is drained by ditches placed at the end of each field. There may also be additional mole or slit drains which are less obvious. Hollows/trenches are separated by ridges/baulks of similar length and width. Additional raised baulks usually exist which were used for access and storage of cut peat. Hollows are often revegetated by hareâ&#x20AC;&#x2122;s tail cotton grass and common cotton grass whilst drier baulks are usually characterised by ling heather, wavy hair grass and birch. If drains become blocked, cutting fields may flood allowing Sphagna to colonise - Sphagnum recurvum is particularly common reflecting enhanced nutrient levels probably relating to peat mineralisation. If the drainage system remains effective, both the baulks and the cutting fields dry out to become dominated by heath vegetation. Many block cut sites are, thus, dominated by leggy heather across the entire site. Species not normally associated with bogs may also colonise these dry peat surfaces such as dock and bracken.

A1.2.6. MILLING Milling was originally pioneered in Scotland in the 1930s. It has subsequently become the most important commercial peat extraction technique and is widely practised in former central and eastern Europe, Scandinavia, Germany and Ireland. Peat is milled to produce horticultural products and fuel for peat fired power stations. Milling is devastating and turns open natural bog into highly drained, bare landscapes (Figure 181


Conserving Bogs

A1.3

YPP Survey and Monitoring Specifications

1.16). Peat is removed layer by layer, gradually stripping away the stratigraphical archive. Additionally, any archaeological finds, which may have been unearthed by extraction, are destroyed by the milling machinery. The first phase of a milling operation involves drainage of the site to allow machinery to pass across the surface. A series of regularly spaced parallel drains (usually 1m wide and 1.5m deep) are dug every 15-20m. These drains are fed into larger collector drains. Sites are often left for 5-10 years prior to further activities. Once the upper peat has dried sufficiently, surface vegetation is removed leaving a bare peat surface. The resulting peat surface is then gently cambered between drains to stop any water collecting on the cutting fields. The top 10-50mm of peat is then rotivated (milled) and left to dry for 24 hours; under dry conditions moisture content drops to 70%. Further drying is promoted by turning the milled peat several times before bulldozing it into long ridges. Peat is then removed from the site. The length and efficiency of the process is weather dependent. In Britain, 8-12 harvests are possible within an extraction season (Wheeler & Shaw, 1995). In Eastern European countries, a more continental climate allows for 20-25 peat extraction cycles (PPA, 1992). Many operations transport milled peat to central processing and packing plants, or direct to power stations, using a network of railway tracks across the bog surface. Milling has severe ecohydrological effects and drastically alters the functioning of a bog. Removal of successive layers of peat gradually lowers the perched water mound whilst intensive drainage of upper peats dries the top surface. However, drainage systems are only designed to dry upper layers and are deepened annually. Following cessation of milling, a layer of wet peat may be left whose hydrophysical properties have altered due changes in water storage capacities and permeability. One important effect of peat extraction is the exposure of underlying darker more strongly humified peat. These 'black' peats suffer greater falls in water-levels than upper, lighter 'white' peats for the same amount of evapotranspiration (Schouwenaars and Vink, 1992). The depth of peat remaining after milling also has an influence. If the bog is underlain by permeable sediments, the site loses water through vertical seepage. Whilst initial depths have not been established, Blankenburg and Kuntze (1987) suggest that at least 50cm of high humification (>H7) peat is required to keep downward seepage losses to an acceptable rate for rehabilitation purposes. The depth of ombrotrophic peat is also important in preventing enrichment from underlying base-rich substrate. Again critical depths have not been established though Eggelsman (1980) again suggests 50cm. However, by taking into account subsurface topography and the final topography required for rehabilitation, several metres of peat may be required; and then of the appropriate quality.

A1.3. AGRICULTURE A1.3.1. INTRODUCTION Peatland areas have long been regarded as wastelands. The wettest areas viewed as hazardous to both man and beast. This has resulted in a desire to reduce the wetness of the areas and if possible to convert them to something regarded as useful and of economic value. As a result, many areas have been drained and/or burnt in an effort to dry the ground and improve the vegetation. Some activities such as re-seeding and/or fertiliser application (particularly after peat cutting), can result in the complete loss of the peatland. Other activities, such as drainage or grazing for example, may cause only a gradual and (possibly) reversible change in vegetation assemblages.

A1.3.2. DRAINAGE Before drainage, fire and grazing were possibly the principal tools for manipulating the vegetation of bogs. With drainage, however, additional advantages have been perceived. Foremost, is the effect on the local water table. Although the drawdown is small, over long time periods, drainage can improve ground conditions to support stock and improve moderately the quality of herbage. Drainage always demands a sustained effort. Drains can quickly infill either through collapse of the peat or through revegetation. Often the gradients on bogs are so slight that unless sophisticated systems of arterial drains are established, there is a strong likelihood of failure. In Britain agricultural subsidies encouraged the expansion of peatland 182


Conserving Bogs

A1.3

YPP Survey and Monitoring Specifications

drainage onto the hill peatlands, though the agricultural benefits from this practice have been negligible or slight. The initial effects of drainage of virgin bog are probably slow to express themselves, but if sustained the following effects can be expected. Ecohydrological effects of agricultural drainage Process Direct drainage

Response  Alters flow patterns.         

Peripheral drainage

 

Dewaters peat body. Increases amplitude of water table fluctuations. Lowers average water table. Increases microbiological activity and hence oxidation of peat. Induces mineralisation of peat and releases nutrients. Changes physical properties of peat e.g. increase in bulk density, compression and subsidence. May induce slumping, irreversible drying and cracking. Encourages a narrower range of bog species (heathers, cotton grasses). Restricts the full range of typical bog mosses resulting in extinctions and replacement by other less typical of open bog. Encourages colonisation by alien species. Lowers perched water table of bog as a whole.

 Alters functional role of lagg fen.

Air photos (see 4.6.6.1) are a very useful tool to identify and locate drains as they show up as distinctive dark, straight lines across the peat. Even when the drains are blocked by vegetation, aerial photographs may still indicate the position of drains as they can remain visible for hundreds of years (Goodwillie, 1980) (Figure A.1). Where drains have become filled in by vegetation, they are less obvious but can usually be picked out by different vegetation associated with the drain line. Distinct lines of bright green aquatic Sphagna or scrub and trees indicate drainlines. The presence of trees or scrub usually indicates some degree of drying out of the surface (in the oceanic conditions of the Atlantic region). Spoil resulting from drain construction can often be identified as a distinct ridge running along one side of the drain. With the passage of time the ridge oxidises and diminishes. The physical wastage (oxidation) of the peat resulting Figure A.1 Revegetated drain which, although infilling, still from drainage is apparent as slumping or acts as an effective drain, Yorkshire Dales, UK. sloping of the ground down into the drain. This physical change occurs alongside all drains but is often not noticeable. The ecohydrological effects described above can also be destructive to archaeological artefacts as well as altering the palaeoecological record contained within the peat (see 1.6).

183


Conserving Bogs

A1.3

YPP Survey and Monitoring Specifications

A1.3.3. GRAZING, POACHING AND ENRICHMENT Introduction Ombrogenous peat is, by definition, poor in nutrients and thus supports vegetation of low nutritive value to grazing animals. Despite this, most bogs are grazed by various animals including sheep (in particular), cattle, deer, rabbits, hares, goats and birds. Some upland farms, in Britain, consist almost entirely of poor quality grazing land, much of which may consist of blanket bog. The impacts of grazing vary considerably especially given its interaction with other forms of land management, notably burning (Rawes, 1983) and drainage. The historical management of blanket bog for the benefit of domestic grazing animals has resulted in a change in species composition and structure. This is exacerbated by increasing grazing pressure from wild herbivores, which, in Scotland, has come largely from the rising populations of red deer (Stainnes et al, 1995). General ecohydrological effects relate to grazing (herbage removal), poaching (trampling) and enrichment. They are summarised below: Process Herbage removal

Trampling

Enrichment

Response  Selective removal of more palatable species at specific times of year (e.g. cotton grass, or tips of purple moor grass).  Encourages growth forms to protect growing tips from grazing.  Encourages species tolerant of grazing pressure.  Damage to microtopography.  Damage to sensitive pool systems.  Exposes bare peat (prevents revegetation).  Creates new niches for alien species.  Increases risk of small scale erosion.  Local enrichment from congregating animals, feeding areas, deaths etc.  Widespread enrichment at high stocking levels.

Grazing Plant species are selectively grazed by herbivores due, in part, to their variable palatability, resulting in uneven structure and composition of communities (Rowell, 1988; Grant et al 1976; Grant et al 1987). Additional variables include grazing species (sheep, cattle etc.), stocking density, composition of habitat, timing and other management practises (such as drainage and burning). Animals browse in various ways and this has differing effects upon the structure and composition of species. Sheep tend to produce an even short sward as they move back and forward across a site. In comparison, cattle tend to produce a more uneven vegetation structure, due mainly to their browsing methods (see Table A.1).

Table A.1 Functional Grazing Attributes of Animals Species

Biting Method

Sheep Red deer Cattle Goats

Biting/shearing Biting/shearing Wrap tongues around vegetation and pull Biting/shearing

Rabbits

Biting/shearing

Selective ability High High Low

Grazing Height Short Short Longer

Highly selective. Very high

Short Very short

The dietary requirements of cattle and sheep vary throughout the year though several communities are commonly selected (Grant et al., 1987). Cattle diets contain a greater proportion of cotton grass than sheep although, in Spring, sheep selectively browse immature flowers of hare’s tail cotton grass. Red deer can exert considerable grazing pressure on upland bog communities. The hinds prefer a similar habitat to those of 184


Conserving Bogs

A1.3

YPP Survey and Monitoring Specifications

sheep providing competition for desirable species and exacerbating damaging impacts of domestic animal grazing. Seasonal variation in species selection is characteristic for all browsing herbivores and is shown in Table A.2. Preference for certain plant communities or species also relates to digestibility at particular times of the year. Table A.2 Selection of Peatland Species by Hill Sheep (M.A.F.F., 1983) Species Selected Ling heather Bilberry Purple moor grass Heath rush Mat grass Hare’s tail cotton grass

Crowberry Deer grass

Parts eaten

Season

Tips Leaves/gree n stems Green

Late summer and late winter Spring - late summer and late winter Early summer

Green Green Young heads

Winter Late winter and spring Late winter and early spring

Leaf butt Green Leaf Green Green

Spring Spring Autumn and early winter Spring

Other observed preferences, not related to digestibility, are also evident and are summarised in Table A.3. Table A.3 Observed grazing preferences not related to digestibility (after Armstrong and Milne, 1995). Species Sheep Red deer Cattle Goats Rabbits

Preferences Avoid mat grass generally but graze small plants as part of a short sword. Avoid rushes. Graze heather more than sheep. Eat more mat grass than sheep or deer. Eat rushes in spring will eat mat grass. Avoid aromatic or prickly species.

The preferential selection by herbivores of desired species imposes uncharacteristic species assemblages and structures. The control of these impacts is largely down to stocking densities, timing of grazing and interaction with other management practices. Poaching Poaching is the term given to damage caused from trampling by animals. Relative levels of poaching are determined by the following:  Animal size - the worst poachers are cattle.  Pressure points - poaching is evident along fence lines, in areas of desirable vegetation, at and around gates and around supplementary feeding stations (see Figure A.2).  Ground conditions - wetter areas are more susceptible.  Vegetation type - Sphagnum is particularly susceptible to trampling.

Another consequence of poaching is the disruption of the physical structure of the surface encouraging areas of bare peat around tussocks.

185

Figure A.2 Poaching damage caused by cattle, Cumbria (Simon Thomas).


Conserving Bogs

A1.3

YPP Survey and Monitoring Specifications

Enrichment Enrichment through grazing may be localised or diffuse. Most enrichment results as a direct input from animal faeces. Usually the addition of faecal matter to an area merely represents a recycling or loss of nutrients rather than any net gain to the system. However, supplementary feeding is often necessary especially during the winter. This can lead to a transfer of nutrients from extra feed onto the bog. Supplementary feeding directly on the bog, in the form of hay bales etc., concentrates enrichment effects (and trampling) around feeding stations. Additionally, animals may be taken in over-night and fed off site. Faeces, deposited on the bog, emanating from overnight feeding also causes a net nutrient gain. Even if grazing is restricted to peatland only, the deposition of nutrients in the form of dung and urine is locally (Rowell, 1988) variable, leading to changes in community composition. Nutrient level increases cause a shift from ombrotrophic to mesotrophic communities (e.g. rushes, Sphagnum recurvum or bog asphodel dominated stands) (see Figure A.3). Another form of enrichment results from decomposition of animal carcasses. Note that, the principal threat to the survival of the archaeological resource lies in possible changes in vegetation allowing the development of deep rooted species or erosion. Enrichment, may stimulate microbial activity which may jeopardise the survival of fragile organic deposits.

A1.3.4. DIRECT IMPROVEMENT – AGRICULTURAL ‘RECLAMATION’ To 'improve' bogs for agriculture, fertilisers are often applied in combination with drainage to boost the nutrient supply available to vegetation. Prior to any fertiliser application, natural vegetation may be flailed to reduce its cover and vigour. Enhanced nutrient status changes vegetation communities and also enables a site to be re-seeded to support an entirely different type of vegetation (pasture or arable crops). Despite fertiliser application, pasture on peat is usually poor and continued fertiliser applications are necessary to avoid a reversion to poor acidic pasture characterised by abundant rush growth. Conversion to agricultural land has had a major impact on lowland raised bogs where the peat has been cut-away. Deep peat areas are more difficult to ‘reclaim’. Where agricultural conversion has been attempted, the land tends to revert to poor acid grassland, often with abundant growth of soft rush, eventually reverting to bog. Re-seeded or heavily fertilised bog stands out as bright green, often fenced areas, generally with a short grassy sward. Extensive areas of soft rush are also indicative of past fertiliser input, particularly where there is a grassy sward between rush tussocks. Depending on the time elapsed since fertiliser applications ceased, there may be elements of heath or bog vegetation reemerging in the vegetation.

Figure A.3 Localised enrichment causes a shift from ombrotrophic to mesotrophic vegetation communities. Isolated stands of bog asphodel are often a good indicator of point source enrichment in the UK.

A1.3.5. BURNING Introduction Fire is used as a management tool to control or manipulate the vegetation of bog peatland in a number of ways. Perceived benefits of burning bogs include: 186


Conserving Bogs

A1.3

YPP Survey and Monitoring Specifications

 Improving the grazing value of herbage for domestic livestock through the provision of spring bite, removal of coarse grasses, preventing the build up of litter (e.g. purple moor grass) and the renewal of heather.  Sustain habitat for red grouse through the provision of a multi-structured and multi-aged heather-rich habitat.

In effect these two objectives are frequently combined in Britain. Fire is also sometimes employed even when the agricultural use has ceased because it is considered “traditional” to do so. Drain clearance and reduction of fire risk to adjacent cash crops is also reported. Malicious fires are a common feature as are accidental ones. The cumulative effects of repeated and regular burning tends to promote a succession which favours heath and grass vegetation communities and suppresses the abundance and diversity of bog mosses. Even without the deliberate use of fire, wildfires or natural fires have occurred at intervals throughout the history of bog development. Such fires have to some degree influenced the development of the vegetation of the British uplands (Stevenson and Thompson, 1995). The magnitude and significance of the effects of fire as an ecological factor remain unquantified, although natural fire frequency is low in comparison to deliberate burning frequency. A long cultural use of peatlands in historic and prehistoric times makes it difficult to separate the effects of natural animal deliberate burning. Evidence of fire can be found throughout the profiles of all lowland raised bogs (e.g. Barber et al., 1993) and blanket bog (e.g. Charman, 1992). Most controlled burning of upland peatland occurs between February and March and is linked to management of heather moorland to improve grazing for sheep and habitat for red grouse. Controlled burning, if conducted in accordance with the Muirburn Code (SNH, 1993), should result in small-scale, low intensity fires. However, uncontrolled burning can be highly damaging to the ecology and economy of peatland areas. The deliberate and continued use of fire in the management of bog vegetation has distinctive ecological effects. These are described below: Process Combustion of vegetation and moss mats and hummocks

Response  Results in complete or partial removal of above ground vegetation.  Promotes a flush of nutrients which may encourage species such as purple moor grass, hare’s tail cotton-grass and deer grass.

Litter & peat combustion

Vegetation succession

 Damages bog moss species which form high hummocks, such as the rare Sphagnum imbricatum. Frequent fires:  expose bare peat creating new niches for species such as S. tenellum; and  increase firmness of the peat which reduces water holding capacity; Intense fires:  remove bog moss mulching layer, altering capacity to modulate precipitation;  expose peat and increase risk of erosion;  consume shallow seed bank; and  form tarry surfaces on peat which reduce water holding capacity. Frequent fires encourage:  shrubs such as heather, crowberry and bilberry;  hypnaceous mosses (Pleurozium schreberi and Hypnum cupressiforme); and  tight cushions of S.compactum, and S. capillifolium, and woolly hair moss. Intense fires encourage  bottle-brush mosses (Polytrichum, Camplyopus etc.), algal mats and crustose lichens; and  unstable and eroding surfaces.

187


Conserving Bogs

A1.3

YPP Survey and Monitoring Specifications

There are several variables which influence the ecological and hydrological responses outlined above. Foremost are the intensity of an individual fire and the frequency of burning. Other variables include, the time of year; the amount of combustible material; and the pattern and speed of fire spread. Intensity The intensity of a fire is controlled largely by the amount of combustible material, though environmental conditions such as moisture content, the position of the water table and wind speeds are also involved. On ground, that is often burnt, the amount of combustible material relates to the time since the last fire. Typical signs of fire include partial or complete scorching and bleaching of bog mosses, charred heather stems and charcoal. Particular bog mosses are considered very susceptible to fire. Sphagnum imbricatum and S. fuscum are considered to be the least tolerant, possibly because they grow in high hummocks. The decline of S. imbricatum on Cors Fochno in Wales, is attributed largely to fire (Slater, 1976). More intense fires may be shown up by partially consumed bog moss hummocks and charring of fence posts and trees, if these occur. Particularly intense fires often lead to the formation of a skin of tarry bitumen formed by chemical reactions following ignition of peat waxes (Mallick, 1979). Crustose lichens such as Lecidea granulosa and Lecidea uliginosa and several species of algae may form over unconsolidated peat, significantly reducing germination rates of seeds (Legg, Maltby and Proctor, 1992). However, algae growths and crusts may serve to prevent excessive erosion across bare peat surfaces. Frequency Regular burning has quite distinctive effects and, in most cases, rather long-lasting impacts on vegetation even if the intensity of fires is low. Regular burning prevents the build up of combustible material in litter and keeps dwarf shrubs in check. Frequent fires also produce flushes of plant nutrients which encourage sedges and grasses. Such flushes are thought to be lost if burning takes place in late autumn or early winter, though the cotton grasses can grow at low temperatures. Plants such as purple moor grass and hareâ&#x20AC;&#x2122;s tail cotton grass, tolerate low and medium intensity fires since their growing bud is usually below ground or well protected in the heart of a tussock. A short fire rotation is considered to favour cotton grasses above heather. Where purple moor grass is present, there may be a build up of litter. Fire is often then used to control this build up. Paradoxically fire favours purple moor grass which can then overwhelm most other species. Less frequent fires at low intensity have more subtle effects. A light, controlled winter burn, for example, removes most of above-ground plant woody material although basal stems of the heather plants remain largely intact, protected by a layer of dead plant material and a wet, or frozen, bryophyte layer. After a fire, heather quickly regrows from both basal stems and seed - the desired objective of moorland management. Effects on other plants are varied. Some species such as purple moor grass, deer grass and hareâ&#x20AC;&#x2122;s tail cotton grass are largely unaffected and if anything are encouraged or favoured by burning regimes given their growth form. A single fire can provide the conditions for the invasion of scrub and trees, while rotational burning destroys seedlings and saplings (Hester and Miller, 1995). Time of Year Time of year affects the temperature of a burn, primarily through the moisture content of combustible material and waterlogging of peat. Autumn fires are thought to encourage heather and may discourage cotton grasses and deer grass. Conversely, later winter fires may stimulate the latter. Summer fires on the other hand are likely to burn hot, risk burning peat and inflict longer lasting damage, for example, through erosion. Other Factors Interactions with other factors such as grazing, hydrology, erosion and climate are also important. The interaction effects of burning and grazing may reinforce the effects of each. Even limited grazing after fire may retard the regeneration of heather. Species which are normally tolerant of fire, such as Cloudberry are likely to be absent given grazing.

188


Conserving Bogs

A1.4

YPP Survey and Monitoring Specifications

Severe burning reduces water storage capacity (Robinson, 1985). This affects the regeneration of many bog species as well as altering the general hydrological behaviour of bog (less water is stored in the upper horizons and discharge following rainfall events may be greater). Erosion, may have a drying effect also. Past erosion and drying may explain the severity of fire in a number of documented cases (for example, Maltby, Proctor and Legg, 1992). Climate, particularly the length of the growing season and exposure, may be an important variable in the regeneration of bog after fire. Recolonisation After Fire The recolonisation of Sphagnum species onto bare peat surfaces is dependent upon:  proximity of available seed (spore) source to bare/burnt area;  hydrological and physiochemical conditions - water table, pH and nutrient status of the bare surface;  ability of different species to colonise from spores; and  ability of different Sphagnum species to compete with other colonising species.

Very little information exists on the ability of Sphagnum species to colonise bare areas although anecdotal evidence suggests that Sphagnum species are poor colonisers. Vegetative regeneration, notably of the aquatic species Sphagnum cuspidatum, provides the quickest method of recolonisation of bare and waterlogged surfaces. Evidence from one study (Lindsay and Ross, 1993) suggests that Sphagnum tenellum is a good coloniser of bare, burnt areas, though this is dependent on both hydrological conditions of the surface being suitable (i.e. wet) and a reasonable community of the species existing in the locality. It is unclear from the study whether colonisation is vegetative or from spores.

A1.3.6. LINT HOLES The cloth production industry has left a legacy on some lowland raised bogs in the form of lint holes (Figure 6.55). These were dug to soak or ‘rett’ flax to remove tough outer layers of the plant and soften the fibres beneath. The acid water of bogs enhanced the procedure, with an added bonus that the process, which was considered smelly and polluting, was carried out away from habitation and also from drinking water supplies. With the decline of the industry, lint holes were abandoned. Lint holes are small (not more than 2-3m across), straight sided and regular shaped. Since the abandonment of the flax industry, at the beginning of the century, most lint holes have filled with vegetation although they often still support a more hydrophilous vegetation than the surrounding peat surface. Aquatic Sphagnum hollows often associated with lush growths of common cotton grass are characteristic. Often the surface is unconsolidated and is unable to bear the weight of a person. These features are small and their impact on a site as a whole is limited. They probably have an effect on water levels immediately around them enhancing shrub growth due to reduced water levels. The effect also relates to their size and distribution - some relatively small sites may have large numbers of lint holes causing a more pronounced effect.

A1.4. COMMERCIAL AFFORESTATION Trees can be a natural component of bog flora. In continental climates of hot and dry summers and cold winters, water-levels fall sufficiently to allow trees to become established although those that do are often rather stunted and often form only sparse cover. In more maritime climates such as those found in Britain, trees are rarely (if at all) a natural component of bog vegetation, although palaeoecological evidence shows that, in the past, conditions on bog surfaces were dry enough to allow tree growth. However, the introduction of the Cuthbertson plough, in the 1950s, allowed deep peats to be drained sufficiently to allow tree planting (see Figure 1.18). Within the U.K., large estates in northern England and Scotland were purchased for forestry leading to substantial areas of upland blanket bog being afforested, e.g. Kielder Forest, Northumberland (England) and the Galloway Forest (Scotland). New tax concessions, set up in 1980 to encourage forestry, were used by private individuals and companies to offset tax losses by investing in forestry. This had the undesired effect of afforesting parts of the Flow Country (this tax 189


Conserving Bogs

A1.4

YPP Survey and Monitoring Specifications

concession was closed in 1988). Raised bogs have been afforested in a more piecemeal way. Large raised bogs in Scotland - e.g. Racks Moss, Lochar Mosses and West Flanders Moss - were afforested in the 1960s and 1970s. Threats from new forestry to British raised bogs have largely ceased. Commercial planting of trees on deep peat has been largely restricted to conifers. The main species used lodgepole pine and sitka spruce - can tolerate a high degree of wetness although some artificial drainage is still required. The simplest form of drainage may be provided by deep ploughing. The young trees are planted on the plough mounds. As trees mature to form a closed canopy, up to 30% of rainfall is intercepted on leaf surfaces (Gash, 1980) significantly drying the peat body. Better initial growth is obtained by utilising systematic drainage systems (see Figure 1.19) where a number of deep drains run into an arterial system (sometimes natural stream courses). The direct ecohydrological impacts of forestry planting are summarised below. Process Ploughing

Drainage

Canopy closure

Fertiliser application

Response  Destroys the acrotelm.  Creates a drier mound inhospitable to bog vegetation.  Encourages non bog species such as wavy hair grass or tussock forming species such as purple moor grass.  Exposes bare furrows acting as drains.  Dries mound further and increases water table drawdown and water table fluctuations.  Increases moisture deficits and lowers summer water table.  Increases mineralisation of peat  May induce slumping of material into drains, scouring, and sedimentation downstream.  Increases interception and evaporation.      

Increases transpiration. Induces cracking. Root development and cracking create new preferential pathways for water flow. Needle fall and canopy shades out most vegetation, except in rides. Peat Compaction. Favours competitive species.

 Increases microbial activity, mineralisation, and runoff of plant nutrients.

Forestry on peatland is not always successful. Foremost is the breakdown of the drainage system. Should this occur prior to canopy closure, tree growth can be set back. If drains infill and become revegetated with bog species, trees may die and the plantation fail. While outright failures are localised, stressed plantations are much more common. Unplanted areas which are surrounded either completely or partially by forestry may also be affected. Smith and Charman (1988) showed that the vegetation of ombrotrophic mire sites in the Kielder Forest - the Border Mires - has changed considerably after the forest was planted. In general, moorland species appear to be outcompeting ombrotrophic bog species. Significant increases of wavy hair grass, Pleurozium schreberi and Polytrichum commune have been matched by decreases in Sphagnum magellanicum, S. papillosum, S. cuspidatum, round-leaved sundew, bog asphodel, common cotton grass, bog rosemary and cross-leaved heath. This could be due to cessation of grazing and burning following afforestation or due to effects of adjacent afforestation on remaining open areas. Long term grazing exclosures have been set up to test this. Initial data analyses suggest cessation of grazing may have a more important role (Charman and Smith, 1992). Run-off from afforested peatlands also affects associated freshwater systems. Palmer (1982) lists a series of effects on watercourses resulting from afforestation on blanket bog:  Run-off: Run-off rates from afforested peat differs from unplanted areas and changes during different stages of afforestation. After initial drainage, run-off is typically ‘flashy’ - quickly peaking and reducing after a rain event (Robinson, 1980). As trees reach closed canopy, run-off decreases due to increased interception and higher transpiration rates by trees. This may result in lowered water levels in associated streams and rivers causing downstream effects on the fauna and flora.

190


Conserving Bogs

A1.5

YPP Survey and Monitoring Specifications

 Sedimentation: Sediment released into water courses increases as a result of increased erosion rates in drained peatlands (Robinson & Blyth, 1982). Enhanced turbidity and silt deposition in streams and rivers also affects plant and animal life.  Fertiliser application: Afforestation also elevates nutrient levels through mineralisation of peat (due to ploughing and drainage) and the addition of fertilisers to encourage tree growth.

Afforestation, commercial or semi-natural, is detrimental to archaeology and the palaeoenvironmental record. Both can be degraded or destroyed due to physical and chemical changes resulting from afforestation. Tree roots can cause physical damage to organic materials and cause microbiological change within the rhizosphere.

A1.5. DEVELOPMENT A1.5.1. LINT HOLES In many cases, the pressure of direct development leads to outright destruction of bogs. However, other types of development may only cause transient changes or only affect part of a peat area.

A1.5.2. ROADS AND RAILWAYS Peatlands have long formed a barrier against travel. The oldest trackways, uncovered within the peat, are prehistoric. The Sweet Track, found in the Somerset Levels, for example, is dated to 3806 BC (Coles, 1995). More recently, peatlands have also proved difficult for road and rail construction. Routes are sometimes 'floated' across bogs using wool bales or birch platforms, although in modern times the preference is to remove peat before construction. Given the extent of blanket bog areas, it is inevitable that roads and railways are routed through peatlands. These routes may have a long history. In the Pennines, pack horse trails, sometimes existing as flagstone paved pathways, have been excavated and restored for use as bridleways. Process Pressure

Drainage

Enrichment

Response to Floating Roads Route sinks. Subsidence/slumping. Local flooding. Compaction. Imposition of new slope on groundwater mound.  Drainage and drying of intact peat.  Drying beneath road - cracking (needing frequent repair).  Local or widespread eutrophication.     

Process Cutting of peat to mineral base

Effluent and nutrient runoff Revegetation of damaged surfaces

 Response to Roads Cutting Through to Mineral  Creates unstable peat face liable to erosion and bog burst.  Dissection or severance of groundwater mound.  New grounwater mound establishes with risk of whole site drying.  Local or widespread eutrophication.  Mixing of peat with mineral soil.  Establishment of rushes 

191


Conserving Bogs

A1.5

YPP Survey and Monitoring Specifications

A1.5.3. HOUSING Housing has had a limited impact on peatlands given that peat is a very unstable substrate for house construction. However, encroachment by housing or industrial estates is encountered. In these cases, peat is stripped away before construction. Clearly, such actions have a dramatic impact on the ecohydrology of the sites in question. The likely effects of house construction are:  Hydrological: Even where peat is stripped away, a site is still likely to be subject to waterlogging and possibly flooding. Housing developments have to incorporate intensive and effective drainage systems disrupting the hydrological regime of the remaining bog. An additional problem is that where peat has been removed from a raised bog, the original shape and size of the peat dome is altered causing further hydrological change (see 2.5.2).  Chemical: Housing adjacent to peatlands may also cause nutrient enrichment either directly as water floods onto peatlands as a result of altered hydrology or indirectly via dust from construction.

A1.5.4. MINING In Britain, there are many peatland areas which overlie economic mineral deposits; coal has had a particular impact in central Scotland, for example. Underground or deep mining creates a network of underground galleries often extending many miles beneath the surface. Once mining has ceased, and mines are no longer maintained, galleries close up and may collapse to result in surface subsidence. One effect of subsidence is the creation of pools as water collects in subsidence depressions. Another effect is the creation of numerous deep and circular depressions (shakeholes) often vegetated by a mixture of grass and dwarf shrub, found, for example, on Conistone and Grassington Moors (Yorkshire, England). Open cast mining is necessarily much more devastating, usually resulting in total destruction of a peatland site. As underlying minerals are usually of greater economic value than peat, the latter is usually removed as quickly as possible. Even where small volumes of peat are removed, they cannot be replaced as the structure and properties are irrevocably modified. Clearly, the archive within removed peat is virtually desroyed as is the context for any archaeological remains which may be found. Rehabilitation work to recreate bog, after mining has ceased, has been tried with little success, although other wetland areas may be created. Ecohydrological effects of mining are: Process Pumping galleries Pumping onto bog surface Collapse of galleries

Dumping or removal of spoil.

Response  Lowers water table in permeable substrates.  Causes drying of bog surface.  Local nutrient enrichment.  Causes subsidence and creates surface depressions.  Depressions may fill with water.  Alters topography of peat surface increasing locally drying effects.  Eutrophication from dust during working.

 Compression of peat, local flooding.

In most cases, the effects of mining are extremely obvious. However, where underground mining has ceased, surface features and historic records should be checked. The presence of numerous large surface depressions, some of which may be water filled, are indicative of deep mining activity. Ordnance Survey maps sometimes mark these depressions as “shake holes”, particularly on blanket bog areas, for example, Conistone Moor (Yorkshire, England). These features should not be confused with “swallow” or “sink holes” which are associated with naturally occurring sub-surface channels on blanket bogs. 192


Conserving Bogs

A1.6

YPP Survey and Monitoring Specifications

A1.5.5. WASTE (RUBBISH) DISPOSAL Peat bogs, having little economic value, have been used as areas for waste disposal. Fly-tipping is a frequent problem on bogs. Further problems are found where agricultural waste has been dumped on bogs. Some raised bogs have been used for tipping local authority waste. Bolton Metropolitan Borough Council, for example, are attempting to use Red Moss SSSI in this way.

A1.5.6. DEVELOPMENT AND ARCHAEOLOGY All of the activities described in Sections A1.5 inevitably result in damage to or destruction of the archaeological resource within peatlands. Outright or partial destruction, hydrological or chemical change, as described above, all impact upon archaeological remains including the palaeoenvironmental record.

A1.6. OTHER FORMS OF DAMAGING ACTIVITY A1.6.1. INTRODUCTION Some activities, if carried out sympathetically, can have a positive effect on a habitat e.g. grouse moor management maintains moorland whilst additional habitats can be created such as open water areas for duck decoys. Others however, can be extremely detrimental to this delicate habitat if not properly controlled. For instance, trampling by walkers has led to severe erosion problems along popular long distance walks which cross blanket peat, e.g. the Pennine Way (Northern England).

A1.6.2. GROUSE MANAGEMENT Large areas of upland blanket bog in Britain are managed for grouse shooting particularly in northern England and southern and eastern Scotland. Grouse feed mainly on young shoots of ling heather or crowberry.. Sporting interests have created heather moorland areas through limited drainage, burning and grazing to increase grouse numbers. This habitat is far from 'natural'. Peat macrofossil diagrams demonstrate that moorlands were originally dominated by Sphagnum mosses and sedges with occasional heathers. However, heather moorland is recognised as a valuable wildlife habitat in its own right and agricultural incentive schemes exist in Britain to encourage its maintenance (for example, the Heather Moorland Scheme). Setting conservation objectives for heather moorland is difficult. For example, British Wildlife reported that Sphagnum growth, which was threatening to overwhelm heather on Dartmoor, could be curtailed by second burning. If the conservation objectives are to work towards more 'natural' systems, the manager would want to encourage Sphagnum growth. However, in this case, the objectives are to manage the peatland as heather moorland rather than as active blanket bog. Priorities may change in blanket bog areas which have been declared as possible Special Areas of Conservation under the EC Habitats Directive. Conservation objectives are clearly defined to conserve active blanket bog.

A1.6.3. SHOOTING AND CLAY PIDGEON SHOOTING Clay pigeon shooting is not a huge problem but is included here as it has been found on some bogs. Main effects relate to trampling and pollution from shattered clays. On Ballynahone Bog (Northern Ireland), for example, shattered clays appear to have altered the chemistry of one part of the site. Poor Sphagnum growth may be due to lead pollution from shot.

A1.6.4. DUCK DECOYS Many duck decoys are quite old although there are also examples of recent attempts to create open water areas for shooting purposes. Duck decoy pools may not have always been deliberately cut some have been created by mining subsidence and peat cutting.

193


Conserving Bogs

YPP Survey and Monitoring Specifications

A1.6.5. TRAMPLING BY PEOPLE A1.7

The physical effect of trampling may be to change the surface microtopography. Hummocks may be destroyed, ridges flattened and depressed to create artificial areas of open water. A good example of the effect of trampling is found near permanent quadrat monitoring stations (see 4.6.3) where peat compression and trampling serves to alter the vegetation being monitored. Repeated trampling, as may occur along footpaths, can cause the total loss of vegetation. In the wet upland areas dominated by blanket peat, the exposed bare peat is particularly susceptible to erosion. This can result in extensive areas of erosion, further exacerbated by people seeking drier routes around the bare, unconsolidated peat, and extending the damaged area (see 1.14 and Figure 5.74).

A1.6.6. VEHICLE DAMAGE In the past, access onto peatland areas would have been primarily by foot although some journeys, particularly to peat banks, would have been made by horse and cart. Damage would, therefore, have been limited to distinct trackways to peat banks. More recently, access onto peatlands may be by tractor or by all terrain vehicles (ATVs). ATVs come in various sizes and designs: some with caterpillar tracks and others with low ground pressure tyres (see 5.6.9) Vehicle traffic on peatlands is associated with both commercial afforestation and some forms of peat cutting such as milling or ‘sausage’ extraction. In these situations, drainage usually precedes other activities to allow heavy machinery to pass safely across the bog surface. However, heavy machinery has been known to sink into peat despite drainage. This often relates to disruption of the peat/water matrix which causes liquefaction of peat to form a highly unstable surface. Increasingly, ATVs are also used to transport people to hunting and fishing sites. This often involves repeatedly using the same tracks. The main forms of damage resulting from vehicle pressure are physical damage to the plants and disruption of the peat surface. Studies on the effect of off-road vehicles on tundra in North America by Richard et al. (1974) have shown that a number of factors are important in determining the degree of damage caused to plants and the peat structure:  Operational and vehicle parameters such as speed, acceleration, wheel-track pressure etc.  Surface topography characteristics - uneven surfaces can become accentuated due to the action of vehicles across an area. On level terrain, compaction or the formation of ruts are common results of repetitive vehicle passes.  Degree of slope - sloping terrain is more susceptible to erosion than level ground and, once initiated, the action of water on bare peat can result in extensive gully formation.  Time of year - damage may be expected to be more severe when the ground is wetter.  Type of vegetation - wet marshy areas experience greater disturbance than well drained areas.  Level of microbial activity - compaction of peat results in increased transfer of heat into, and out of, the underlying soil which may alter the rate of microbial activity.

A1.6.2. MOSS GATHERING Sphagnum moss absorbs water extremely well. As a result, Sphagnum has been put to a variety of differing uses. In the past it has been used as a sterile dressing, filling for babies nappies and to clean up oil spills and other contamination. More recently, large quantities of Sphagnum moss are used in the horticultural industry. Wet Sphagnum is often used as a packaging around plants during transportation. In a dry state, it is used to line hanging baskets, as, once wetted, it releases water to growing plants at a slow and steady rate. Sphagnum also prevents the growing medium, contained within the hanging basket, from drying out too quickly. Sphagnum moss is an important component of a functioning acrotelm (surface layer). Its removal, therefore, can have a considerable damaging impact. Terrestrial Sphagnum removal exposes bare peat, causing drying (through higher evaporation rates) and erosion. Removal of aquatic species from pools has less effect, although if aquatic species are removed from re-vegetating drains, the drain is likely to become more efficient. 194


Conserving Bogs

A1.7

YPP Survey and Monitoring Specifications

A1.7. INDIRECT FORMS OF DAMAGE A1.7.1. POLLUTION Bogs are rain-fed, and thus nutrient poor, making them particularly vulnerable to the effects of chemical pollution. Pollutants may enter the system in a variety of ways:  via the atmosphere: fertiliser drift from agriculture and forestry or acid deposition from industrial activities and vehicle emissions.  via drains or surface run-off: agricultural effluent, sewage, industrial waste etc.  via direct application: fertiliser for agricultural improvement, liming, manure etc.  via faecal enrichment: from bird roosts, grazing animals etc.

Atmospheric Pollution The addition of nutrients and pollutants from the atmosphere may have an effect on both the development of peat and the vegetation of a mire. There are three main sources of atmospheric nutrient enrichment: the surrounding land, industry and the sea. Glaser and Jaansens (1986), for example, consider the surprisingly Sphagnum-rich bogs of mid-continental Canada to be the result of dust from the North American prairies fertilising the bogs to favour the growth of Sphagnum over lichens. Further, Van Geel and Middledorp (1988), attempting to explain the local extinction of Sphagnum imbricatum from Carbury Bog, Eire in ca. 1400 AD, note that this may be related to the intensification of agriculture, reflected in the pollen diagram, increasing dust and charcoal aerosols. Rudolf and Voigt (1986) have shown that for several Sphagnum species a nitrate concentration of 100µM is favourable but that Sphagnum magellanicum can tolerate up to 322µM. This may explain the increase and dominance of Sphagnum magellanicum in recent peat layers at Carbury Bog and also at many other sites in the U.K. Stoneman et al. (1993) and Stoneman (1993) also found evidence to suggest that agriculturally derived atmospheric nitrogen deposition may have caused the decline of Sphagnum imbricatum across the British bogs. In the southern Pennines, Moss (1913) listed eighteen Sphagnum species of which only two were rare. By 1964, Tallis recorded only five Sphagnum species of which only Sphagnum recurvum was common. Industrial pollution may have had a significant effect on the ecology of the southern Pennine blanket peatlands. Conway (1948) found that at Ringinglow Moss, Derbyshire, Sphagnum disappeared when industrially derived soot spheres became prevalent. The sensitivity of Sphagna to industrially derived sulphur pollution is well documented (Ferguson et al., 1978; Ferguson and Lee, 1979 Ferguson et al., 1984; Press et al., 1986). Twenhoven (1992) looked at the effect of nitrate and ammonium addition on Sphagnum magellanicum and Sphagnum fallax (Sphagnum fallax is known as Sphagnum recurvum in Britain) on a mire in Germany. Where pollution is low, the two species occupy a similar niche and are often found growing together. The addition of nitrogen however, caused Sphagnum fallax to out-compete Sphagnum magellanicum in hollows and on lawns. On hummocks, the better water holding capacity of Sphagnum magellanicum allowed the moss to out-compete Sphagnum fallax during drier periods. Increased atmospheric nitrogen deposition may therefore, explain the recent success of Sphagnum fallax across Central Europe and NE Europe. It is worth noting that the only Sphagnum species found on much of the southern Pennines is Sphagnum recurvum (Ferguson et al., 1978). Deposition of minerals can affect bog ecology. In the southern Pennines there seems to be a fairly clear connection between Sphagnum decline and industrial and agricultural pollution. Elsewhere in the U.K., the decline of Sphagnum imbricatum with a concurrent increase of Sphagnum magellanicum and Sphagnum papillosum may also be due to pollution (Stoneman, 1993). Eutrophication Elevated nutrient levels (eutrophication) results in increased plant growth rates and species change which in turn has significant effects on numbers and types of micro-organisms present (Maltby, 1992). This can lead 195


Conserving Bogs

A1.7

YPP Survey and Monitoring Specifications

to changes in decomposition rates possibly preventing peat formation. Enrichment may come from a variety of sources: farm waste, domestic refuse, sewage, road surface water drainage and bird roosts.

A1.7.2. CUMULATIVE IMPACTS Theoretically, both raised and blanket bogs are stable climax systems (Godwin, 1975, Moore 1987). Occasionally, natural perturbations occur (fire and bog bursts etc.) which temporarily disrupt the equilibrium; although, with time, a stable state re-establishes. Bog sites in their natural and undamaged state, therefore, do not require active management to sustain a natural vegetation cover. However, sites are often encountered where the vegetation cover is distinctly unnatural yet there are no obvious forms of damage. On these sites, it is highly likely that there has been damage although it was so long ago the direct evidence is difficult to discern. Drains, for example, may be well-vegetated but still function well. Past fertiliser application and past repetitive burning are also often difficult to identify yet may still be affecting the site's ecology. Atmospheric pollution and changes in surrounding water levels are particularly difficult to isolate as causal agents for ecological change although they may have profound effects. In Britain, at least, every raised bog in the country and most areas of blanket bog have been damaged in some way. Areas of seemingly 'near-natural' vegetation are nearly always surrounded by more damaged areas. As different parts of the same bog are intimately connected through the same hydrological systems, damage in one area of a site is likely to affect another (see 2.5). Consequently, many sites are probably continuing to degrade due to forms of damage that may have occurred many years ago.

196


Conserving Bogs

YPP Survey and Monitoring Specifications

APPENDIX 2 YORKSHIRE PEAT PARTNERSHIP SURVEY AND MONITORING SPECIFICATIONS A2.1 Pre Survey A2.2 Field Survey A2.3 Post Survey A2.4 Diagrams of dam constructions A2.6 Monitoring Protocols A2.7 Peat Physical Characteristics A2.8 Monitoring Considerations A2.9 Remote monitoring A2.10 Overall Summary A2.11 Detailed Von Post Scale for Classification of Humification A2.12 Data Transfer, Storage and Manipulation A2.13 Site Details Recording Form A2.14 Peat Physical Properties Field Form A2.15 Vegetation Height Recording Form A2.16 Vegetation Species Recording Form

YORKSHIRE PEAT PARTNERSHIP SURVEY SPECIFICATION MAY 2012 197


Conserving Bogs

A2.1

YPP Survey and Monitoring Specifications

A2.1. PRE SURVEY Create GIS layers as follows: 1. 2. 3.

4. 5.

6. 7. 8.

9. 10. 11.

GRIPS: Map grips from high resolution aerial photographs map. NATURAL WATERCOURSES: Map all natural watercourses from high resolution aerial photographs to match those classed as in blue on the Ordnance Survey 1:25000 maps. BARE PEAT: Map bare peat using spectral analysis in ArcGIS using YPP protocols (Brown, 2012). Extract gully bare peat and hag bare peat from this to provide a final map showing flat bare peat. ERODING GULLIES & WATERCOURSES: Using the bare peat map as a guide create a linear map showing all gullies with eroding sides. GULLY BARE PEAT: Create a 10m buffer around the gullies in the eroding gullies map and overlay this with the bare peat map to select bare peat associated with gullies. Save this as a Gully Bare Peat map HER: Obtain Historic Environment Record for each site. ISOLATED HAGS: Using the bare peat map as a guide create a linear map showing all isolated hags with eroding sides. ISOLATED HAG BARE PEAT: Create a 5m buffer around the hags in the isolated hags map and overlay this with the bare peat map to select bare peat associated with isolated hags. Save this as an Isolated Hags Bare Peat map EXTENSIVE HAGS: Using the bare peat map and eroding gully map as a guide create polygons around extensive hag zones. EXTENSIVE HAGS BARE PEAT: Overlay this polygon with the bare peat map to select bare peat associated with extensive hag zones. Save this as an Extensive Hags Bare Peat map FIELD SURVEY TRANSECT: Overlay site boundary with 100m grid. Using this grid mark sampling locations every 200m.

Load maps onto GPS enabled field computer.

A2.2. FIELD SURVEY 1. Habitat recording: At each sampling point along the field transect record the following information into the GPS enabled field computer: -peat depth (m) -heather height (m) over a 5m x 5m area <15cm, 15-30cm, >30cm. -vegetation community class viewed over a 2m x 2m area (Table 3) -all indicator species present in a 2m x 2m area (Table 4) -Nanotope type in a 5m x 5m area (see Table 5) -burning category in a 5m x 5m area (see Table 6)

2.

Grips & Gullies : Whenever the transect crosses or passes within 1m of a grip or gully record the following information into the GPS enabled field computer:

-flow present YES/NO -dams present YES/NO -grip category (see table 8) 198


Conserving Bogs

A2.3 33

YPP Survey and Monitoring Specifications

-gully width category (see Table 1) estimated from peat side to peat side at the widest point of the vertical profile -gully depth category (see Table 2) estimated from the base of the grip/gully in the middle to the top. -base type as mineral (m), peat (p) or vegetated (v). -eroding base as YES/NO -eroding sides as YES/NO Angle of sides as vertical, ≥750 (v), severe, ≥450 <750 (s) moderate, ≥330<450 (m) Sphagnum present YES/NO 3. Hags: Whenever the transect crosses or passes within 1m of a hag record the following. In areas of extensive hagging where the transect is passing continuously through hags do this recording every 100m. -height of the hag above current ground level (m) -vegetated on top YES/NO -vegetated between hags YES/NO -erosion between hags YES/NO -eroding sides YES/NO -Angle of sides as vertical, ≥750 (v), severe, ≥450 <750 (s) moderate, ≥330<450 (m) -Sphagnum present between hags YES/NO -Sphagnum present on top of hags YES/NO 4. Historic Environment recording: Record all HE features (as GPS centroid points with an estimate of size) seen during the walkover (see Table 7). 5. Soil analysis: Take 25 small peat samples (using “cheese-corer” soil sampler) from areas of bare peat which should be combined to produce 1 sample for each site. These samples should then be sent to a laboratory to be tested for pH and nutrient levels.

A2.3. POST SURVEY 1.

Grips: Using high resolution photographs as a base map and the information collected on grips in the field digitise lengths of grips into a MAPINFO table according to the classification outlined in Table 8.

2.

Gullies & Category 4-6 grips: Using the gully widths map created in the Pre-survey and the map of Category 4-6 grips together with the field data on gully/large grip characteristics classify these further into linear sections within MAPINFO as described in Table 9.

3. Extensive hag zones: Using the pre-survey and field data on extensive hag zones classify these into polygons in MAPINFO based on the criteria in Table 10.

4. Habitat: Create a MAPINFO point table showing the different vegetation community classes at each sampling location (we plan to use this information in future in an image classification study to eanable habitat areas to be mapped from aerial photography)

5. Species: Create a series of MAPINFO point tables showing the distribution of Sphagnum mosses and the following other indicator species: 199


Conserving Bogs

A2.3

YPP Survey and Monitoring Specifications

-Calluna vulgaris (Heather) -Eriophorum angustifolium (Common cottongrass) -Eriophorum vaginatum (Hare’s-tail Cottongrass) -Erica tetralix (Cross-leaved heath) -Empetrum nigrum (Crowberry) -Molinia caerulea (Purple-moor grass) -Juncus effusus (Soft rush) 6. Nanotope types: Create a MAPINFO point table showing the different nanotope types at each sampling location (we plan to use this information in future in an image classification study to enable explore whether nanotopes can be mapped from aerial photography) 7.

Heather heights: Create a MAPINFO point table showing the heather heights at each sampling location.

8. Historic Environment: Create a MAPINFO point table showing all features of historic environment interest. 9. Services: Carry out searches to determine whether any services (water pipes, electricity cables, gas pipes) cross the site and identify these on GIS maps. 10. Access: After discussions with stakeholders identify access routes & “no-go” areas for machinery and map these. 11. Locations for materials storage/lift sites: Identify these on maps after discussions with stakeholders.

200


Conserving Bogs

A2.3

YPP Survey and Monitoring Specifications

Table 1: Gully Width Categories Class 1 2 3 4

Gully Width (cm) ≤1m >1m≤2m >2m≤3m >3m

MapInfo colour code Blue (I1) Pink (J1) Yellow (F1) Green (G1)

Table 2: Gully Depth Categories Class 1 2 3

Gully Depth (m) ≤1m >1m≤2m >2m≤3m

Table 3: Vegetation communities Community BB75 BB50 BB25 HD WD AGM AGJ AGN AGJN NCG BR AF BF BP BM

Description Blanket Bog >75% dwarf shrub Blanket Bog ≥25%≤75% dwarf shrub Blanket Bog <25% dwarf shrub Dry heath Wet heath Acid Grassland (Molinia caerulea) Acid Grassland (Juncus squarrosus) Acid Grassland (Nardus stricta) Acid Grassland (Juncus squarrosus/Nardus stricta mosaic) Neutral/Calcareous Grassland Bracken Acidic Fen Basic Fen Bare Peat Bare Mineral

201


Conserving Bogs

A2.3

YPP Survey and Monitoring Specifications

Table 4: Indicator species Code Cv Ea Ev Sc Et Em Vm Vv Vo Rc Ap No Dr Mc Je Sph Sfa Spp Scp Sm Scu Spu Ss St Saf Sau Si Sfu Sq Sd Pc

Species Calluna vulgaris (Heather) Eriophorum angustifolium.(Common Cottongrass) Eriophorum vaginatum (Hareâ&#x20AC;&#x2122;s-tail Cottongrass) Scirpus cespitosus (Deergrass) Erica tetralix (Cross-leaved heath) Empetrum nigrum (Crowberry) Vaccinium myrtillus (Bilberry) Vaccinium vitis-idaea (Cowberry) Vaccinium oxycoccos (Cranberry) Rubus chamaemorus (Cloudberry) Andromeda polifolia (Bog Rosemary) Narthecium ossifragum (Bog Asphodel) Drosera spp. (Sundew) Molinia caerulea (Purple-moor grass) Juncus effusus (Soft rush) Sphagnum species Sphagnum fallax Sphagnum papillosum Sphagnum capillifolium Sphagnum magellanicum Sphagnum cuspidatum Sphagnum palustre Sphagnum subnitens Sphagnum tenellum Sphagnum affine Sphagnum austinii Sphagnum inundatum Sphagnum fuscum Sphagnum quinquefarium Sphagnum denticulatum Polytrichum

202


Conserving Bogs

A2.3

YPP Survey and Monitoring Specifications

Table 5. Nanotope type.

203


Conserving Bogs

YPP Survey and Monitoring Specifications

A2.3

204


Conserving Bogs

YPP Survey and Monitoring Specifications

A2.1

Table 6: Burning classes Class 0 1 2 3 4 5

Description No burn New burn – blackened vegetation 1-5 year old burn – heather regenerating but not closed canopy 5-10 year old burn – closed canopy pioneer heather (up to 15cm high) Mature heather between 15 and 30cm high Tall old heather

Table 7: HE record Code N U E T1 T2 T3

Description HER feature not noted on ground or absent Upstanding feature – e.g. boundary stone, walkers cairn, sheepfold Earthwork feature, e.g. peat cutting, mineshaft or prehistoric cairn Tree remains - single Tree remains - multiple Tree remains - abundant

Table 8: Grip classes Class 1b 1f 2 3 4 5 6

Description Blocked grip up to 600mm wide; 650mm deep Flowing grip up to 600mm wide; 650mm deep Early erosion; >600mm-1000mm wide; >650mm-1000mm deep Eroding and deeply scoured: >1000mm-1500mm wide; >1000mm-1200mm deep. Grip which is wide in relation to depth: >1500mm-2000mm wide; >1200-2000mm deep No longer a grip, now a watercourse with bare peat edges: >2000mm-3000mm wide; 2000-3500mm deep A huge washed out grip: >3000mm wide; >3500mm deep.

205


Conserving Bogs

A2.3

YPP Survey and Monitoring Specifications

Table 9 Post-survey gully classification Gully/large grip class 1a 1b 1c 1d 1e 1f 2a 2b 2c 2d 2e 2f 3a 3b 3c 3d 3e 3f 4a 4b

Description Width ≤1m

Depth ≤0.5m

sides severely sloping/vertical sides moderately sloping sides severely sloping/vertical sides moderately sloping sides severely sloping/vertical sides moderately sloping sides severely sloping/vertical sides moderately sloping sides severely sloping/vertical sides with moderately sloping sides severely sloping/vertical sides moderately sloping sides severely sloping/vertical sides moderately sloping sides severely sloping/vertical sides moderately sloping sides severely sloping/vertical sides moderately sloping sides severely sloping/vertical sides moderately sloping sides

>0.5m≤1m >1m >1m≤2m

≤0.5m >0.5m≤1m >1m

>2m≤3m

≤0.5m >0.5m≤1m >1m

>3m

All

Table 10 Post-survey extensive hag zone classification Gully/large grip class

1a 1b 1c 1d 2a 2b 2c 2d 3a 3b 3c 3d 4a 4b 4c 4d

Description

Description

Hag Height

Eroding Sides

≤1m

NO

Vegetated between YES NO

YES

YES NO

>1m

NO

YES NO

YES

YES NO

206

Vegetated on top YES NO YES NO YES NO YES NO YES NO YES NO YES NO YES NO


Conserving Bogs

A2.4

YPP Survey and Monitoring Specifications

A2.4. DIAGRAMS OF DAM CONSTRUCTIONS

207


Conserving Bogs

YPP Survey and Monitoring Specifications

A2.4

208


Conserving Bogs

YPP Survey and Monitoring Specifications

A2.4

209


Conserving Bogs

YPP Survey and Monitoring Specifications

A2.4

210


Conserving Bogs

YPP Survey and Monitoring Specifications

Yorkshire Peat Partnership vegetation and peat physical characteristics protocol

From the Yorkshire Peat Partnership September 2011

211


Conserving Bogs

A2.5

YPP Survey and Monitoring Specifications

A2.5. VEGETATION AND PEAT PHYSICAL CHARACTERISTICS Summary protocol overview: The following protocols are suggested as the basis for the Yorkshire Peat Partnership vegetation and peat physical characteristics monitoring protocol. The purpose of the protocol is to enable the collation of detailed vegetation variables and peat physical characteristics to provide a detailed dataset on the impact of peatland restoration techniques including drain blocking and revegetation on the peatland ecosystem. Some of the data collected will act as useful proxies for other environmental variables such as the water table in the absence of direct measurements. It is designed to be carried out by skilled volunteers to ensure that changes in peatland condition can be assessed in the long-term. The following sections detail brief overviews of the methodologies which will be implemented by the Yorkshire Peat Partnership. Fixed point photography:  A series of before and after fixed point photographs detailing restoration works.  Fixed point photographs of works of specific interest such as the trialling of new revegetation or dam techniques.  Photographs of anomalous events such as extreme weather and floods that may influence or compromise the success of restoration works. Vegetation monitoring design: Ideally, random samples will be taken across the restoration site to obtain optimum statistical validity. However, random sampling involves a huge degree of time and resources to implement to ensure validity. The heterogeneity of bogs is a compounding factor making statistically robust random sampling in a peatland ecosystem even harder to achieve. Consequently, permanent quadrat monitoring is suggested as the most effective monitoring strategy for Yorkshire Peat Partnership restoration sites. Vegetation sampling design: A belt transect will be set out perpendicular to the blocked grip (0.5m x 2m) and adjacent to any dipwells that may be installed. The length of the transect will be no less than 2m perpendicular to the blocked grips, so spanning across the peatland. 1m x 1m quadrats will be placed at regular intervals along the transect. Permanent quadrats will also be established on bare gripped and peat areas. A series of permanent quadrats (2m x 2m) will also be established across the wider peatland area to assess trends in environmental variables across the wider peatland habitat. The number of transects laid and quadrats recorded will be determined by site area, grip density and distribution, site topography and statistical validity. Percentage cover of the bryophyte layer, the herb layer and the shrub layer will be assessed using the following methodology; 

Divide the transect into 25 cm squares and record percent cover for each square. This will achieve greater accuracy when recording the bryophyte layer. Take a photograph of each quadrat along the transect.

Lay out the transect again and divide into 10cm squares and record percent cover in each quadrat. This will achieve greater accuracy when recording the herb layer. Take a photograph of each quadrat along the transect.

For taller vegetation (e.g. heather) lay out and photograph the transect as above and record percent cover of species at 10, 20, or 25 cm intervals along the centre line of the transect depending on the 212


Conserving Bogs

YPP Survey and Monitoring Specifications

time available and the nature of the vegetation. For example, big, dense, tall species composition may only be practical at 25 cm intervals. Take a photograph of each quadrat along the transect.

A2.5

For each of the three layers recorded, the maximum height of each plant layer must be recorded.

Percentage bare peat present will also be estimated.

This methodology enables the accurate recording of vegetation species from each vegetation layer which will generate a picture of the vegetation structure. If the above methodology is impractical due to time and/or technical constraints, the percentage cover of each of the three vegetation layers could be measured within a 2m x 2m quadrat laid out at 5m intervals but this may yield less accurate results. Monitoring frequency: Restoration sites will be revisited and monitored on an annual basis, preferably in July (access permitting) as this is the optimum time floristically for surveying. As this is infrequent, the resolution of species monitoring as suggested above is viable as monitoring intensity is high but frequency is low. Monitoring recording: All monitoring transects and fixed point positions will be recorded using GPS to accurately mark locations. Ideally, belt transects will be positioned perpendicular to both blocked grips and preferably unblocked or revegetating grips on the same site as control monitoring sites. Ideally, all data will be recorded using GPS, however, this may not be possible due to volunteer numbers and equipment limitations so a series of field recording sheets have been developed. Proxy’s using vegetation and topography: The purpose of implementing such a detailed vegetation monitoring protocol is that the data generated provides information that can be used to assess other peatland variables such as water table and gradients, carbon storage potential and greenhouse gas fluxes. Water table, gradient and movement: Patterns of nanotopes (fine-scale topographical and habitat classifications, see protocol section below) can give a very clear indication of gradient and relative rate of water movement. Additionally, each nanotope is characteristic of a particular moisture range and consequent peat density at that specific point (Lindsay 2010). For more detailed information on water table characteristics associated with nanotope form see table 1. It is possible to make accurate inferences regarding the status of the water table if nanotope form is accurately recorded. Vegetation monitoring and green house gas flux:  Allows for fine scale mapping.  Is responsible for part of the GHG emission itself due to the quality of the organic matter it produces and by providing possible pathways for increased methane emissions.  Is controlled by the same factors that determine GHG emissions from peatlands such as acidity, nutrient availability).  Reflects longer term water level conditions and therefore provides and indication of relative time scale. (Cited form Bonnett et. al., 2010, adapted from Joosten and Cowberg, 2009). Currently, there is research is being undertaken on the relationship between vegetation type and greenhouse gas emission: Green House Gas Emission Site Types GEST (Haans Joosten 2009). This research further informs the relationship between vegetation type and green house gas flux substantially increasing the accuracy of the proxy. Net Primary Production (NPP): Estimates of plant biomass and plant carbon content can be used to determine the input of carbon via net primary production. The estimation of NPP is complex and specific to 213


Conserving Bogs

A2.6

YPP Survey and Monitoring Specifications

different vegetation types. It is dependant on the extent of lignification and different growth strategies. However, a list of techniques for different vegetation types is available and can be incorporated into baseline monitoring to provide an approximate estimate of the impact of restoration on peatland carbon storage potential. There are a number of different NPP measurement techniques for example; Sphagnum NPP can be measured using the crank wire technique. This technique will be applied to areas of Sphagnum present within designated belt transects and/or fixed quadrat locations. If this is not possible, it may be necessary to locate areas of Sphagnum dominance outside of the fixed monitoring locations in order to implement requisite Sphagnum NPP measurements (see Clymo 1970, Sala et. al. 2000 and Vitt 2007 for methodologies). Crank wire method: The crank wire method enables measurement of Sphagnum growth. The equipment required is relatively simple consisting of a bar with wires inserted perpendicular to the bar at regular intervals. The wires are usually about 30 cm in length and are approximately 1-5mm thick with a 2cm bend in the middle. The purpose of the bend is to prevent the wires from being pulled out. A spirit level can be used to ensure that the position remains constant. A decrease in the in the distance from the top of the wire to the Sphagnum surface is used to determine growth in length. For this method, specific patches of Sphagnum need to be targeted for measurement. There are some assumptions that need to be taken into account when applying this method in the field; ď&#x201A;ˇ ď&#x201A;ˇ

The weight of the capitula of the plants do not change in weight over the study period. The uppermost 1 cm of the increment is representative of total annual growth increment.

A2.6. MONITORING PROTOCOLS Introduction: The following sections detail the protocols and guidance for data interpretation that will be used by the Yorkshire Peat Partnership as part of the monitoring protocol. The protocols include microtopographical features, indicator and bryophyte species. Overall, the aim of the protocols is to aid the interpretation of observed changes in environmental variables in relation to restoration works. Microtopographical features: Nanotope analysis is a vital component of the Yorkshire Peat Partnerships monitoring protocol as they can give a clear indication of gradient and relative rates of water movement. Of great value when interpreting the data is that each nanotope which form the components of the microtope is characteristic of a specific moisture content and therefore peat density at that measured point (Lindsay 2010). Simply, nanotope can be divided into three terrestrial and three aquatic microform types and they occupy a specific height zone relative to the mean water table. They are highly sensitive to changes in the water table so if the site is disturbed and there is water table draw down then terrestrial nanotopes will expand at the expense of the more aquatic nanotopes and vice versa. Microtope form will be assessed at each of the fixed quadrats and quadrats located along the length of the belt transect. In order to effectively interpret vegetation changes in relation to nanotope form individual quadrats should ideally be representative of a single microtope zone. Location of the quadrat and nanotope form will be recorded using GPS.

214


Conserving Bogs

A2.6

YPP Survey and Monitoring Specifications

Table 11. Nanotope type, description and water table characteristics (Lindsay 2010) Nanotope type Description Water table characteristics Re-vegetation of any erosion gully or N/A E1 section of gully showing signs of Revegetation revegetation. E2 Erosion gully actively eroding, so significant N/A Active erosion revegetation. Em1/2 Evidence of impact on bog surface; N/A Micro erosion burning, grazing, trampling etc. Formerly eroded but undergoing N/A Tk tussock significant vegetation recovery. Vertical range of 0-15cm. Highest prop of 0 – 15 cm above average water T1 Low ridge Sphagnum, richest zone for characteristic table bog species. 15-25cm, characterised by bog and some 15-25 cm above average water T2 High ridge heath species, Sphagnum cover variable. table 25cm-1m. some bog species and several 25cm – 1m above average water T3 Hummocks heathland species, notably heather. table Supports several heathland spp, and 1 or 2 T4 erosion hags bog species, dwarf shrubs and lichens Vertical zone 0.75m – 1m+ common. 0-10 cm, species poor, dominated by S. A1 Sphagnum 0cm - -10cm below average cuspidatum, perhaps stands of cotton hollows water table grass. A2 Mud bottom Shallow pools no more that 20 cm deep, Shallow pools no more than 20 hollows mud or decomposed vegetation for base. cm deep The options above offer an extensive list of microtope formations. By classifying the nanotope the microtope type can be classified which will inform water table depth. These nanotopes can be assembled into microtopes which are an important as they can give a clear indication of gradient and relative rates of water movement (for a full and detailed description of nanotopes and microtopes see last appendix of Richard Lindsay 2010 publication entitled “Peat Bogs and Carbon – a critical synthesis”). See Appendix 4 for an Illustration of nanotope forms that can be used in the field (R.A., Lindsay 2010). Table 12. Methane emissions and nanotope estimated by Laine et. al. (2007) from differing parts of blanket bog in Co. Kerry, Ireland (adapted from Peatbogs, a critical synthesis by Richard Lindsay 2010).

Nanotope

T3 Hummock T2 High Ridge T1 Low Ridge Non vegetated A2 hollows Vegetated A2 hollows

Annual CH4 emissions (g CH4 m-2 yr-1) 3.3 5.8 6.1

Daily CH4 emissions (mg CH4 m2 yr-1) Average Range

Median Water level (cm)

11.8 19.2 20.9

0.1-64.1 0.0-72.2 0.1-101.4

-13 -5 -1

3.5

11.6

1.7-31.8

3

13.0

50.4

0.3-263.0

5

215


Conserving Bogs

YPP Survey and Monitoring Specifications

This table can be used to very broadly infer green house gas emissions relating to nanotope forms, taking into account all the caveats associated with extrapolating data to different regions.

A2.6

2.3. Indicator species: Indicator species and the functional characteristics can be used to assess the condition of and changes within the peatland environment. There are a number of different species types that can be used to assess changes in condition (Bardsley et. al. 2001);  Keystone species- contribute to physical form of the habitat e.g. Sphagnum.  Definitive species – those that define a habitat.  Characteristic species – usually present within the habitat.  Dominant species – Species that dominate the habitat.  Indicator species – species that can react to changes in habitat condition.  For the purpose of the Yorkshire Peat Partnership monitoring objectives, indicator and keystone species will be the main focus of the protocol. Table 13. Potential indicator species for the vegetation monitoring strategy. Vegetation species (desirable bog spp) Notes/attributes Eriophorium spp (esp angustifolium) * Increase suggests increased wetting and may invade precursor floating Sphagnum carpets or root directly into peat. Calluna vulgaris* Only an indicator of “success” if associated with other peat forming sphagna. Constant wet heath species. Erica Tetralix* Only an indicator of “success” if associated with other peat forming sphagna. Constant wet heath species. Drosera spp Peat bog species Weed species including birch/pine/molinia Reduction in vigour would be regarded as indicative of success. Vegetation species (undesirable bog spp) Notes/attributes Juncus effusus May indicate eutrophication problem and/or disturbance. Birch/pine Invasion probably indicates that conditions are too dry. Calluna/Molinia Invasion probably indicates that conditions are too dry. Any fen species Indicates a minerotrophic water source. Weed species e.g. Bracken Suggests conditions are too dry and possibly disturbed. (Adapted from YPP pre restoration survey, Monitoring raised bogs NE report, Wheeler and Shaw 1995, Phase III Moorland Report, Penny Anderson 1997.* Species and genus percentage cover measured as part of YPP pre-restoration survey). Interpretation of species data using indicator species as guidance allows for changes in not only species but also functional characteristics of the peatland. This information coupled with different restoration impacts may further inform any trends or changes in datasets. Bryophyte species list: Current knowledge to the exact level of indication of Sphagnum species does not suggest that there is enough empirical evidence to have a comprehensive condition assessment using Sphagnum as a management indicator. However, distinguishing between peat forming and non-peat forming 216


Conserving Bogs

A2.6

YPP Survey and Monitoring Specifications

species is a very useful indicator of condition assessment and current state of the peatland and some inferences in accordance with the presence of certain species can be made.

Table 14. Bryophyte indicator species list for the vegetation monitoring strategy. Bryophyte species Notes/attributes Sphagnum cuspidatum Colonise areas with open standing water, a decrease suggest drying out of pools * S. recurvum Increase may suggest enrichment and/or pollution. S. fimbriatum Could indicate base or nutrient enrichment S. squarrosum Could indicate base or nutrient enrichment S. papillosum Indicates satisfactory development of bog species. Decrease suggests drying out. S. magellanicum Indicates satisfactory development of bog species. Decrease suggests drying out. S. capillifolium Increase at the expense of other Sphagnum spp suggests drying out * S. tenellum Increase may suggest recovery from fire or trampling. S. fallax Is tolerant of elevated pH and nutrient status and retains competitive advantage over a wide range of condition. Also may indicate recolonisation of bare ground as it is a pioneer species. S. compactum Increase suggests a drying or recovery from burning. S. subnitens Possibly may suggest and increase in nutrient status. S. imbricatum (S. austinii, & S. affine, S . fuscum) Decrease may possibly suggest excessive burning. * indicates that the management indicator is reliable according to an evaluation of available scientific literature based on an evaluation of scientific literature (cited from Peatscapes project: Sphagna as management indicators research, Final report, North Pennines AONB Partnership, Ptyxis Ecology 2008). The above table can provide a guide to interpreting any changes in Sphagna frequency and distribution in relation to restoration. The following table relates vegetation types to Green House Gas emissions. Such data could allow us to make broad inferences about green house gas emissions status on restoration sites. Table 15 – Vegetation types in Ostrovskoe and Vygonoshanskoe with associated flux measurements and their standard deviations and best estimates of GWP. Vegetation type CO2 CH4 GWP Remarks Bare Peat 7.0 (± 2.6) for 0.4 (±0.6) for 7.5 active extraction active extraction sites. sites. 7.4 (± 0.9) for 0.06 (±0.0) for abandoned abandoned extraction sites. 1. extraction sites. 1. Calluna As moist bog heath 12.5 217


Conserving Bogs

A2.7

YPP Survey and Monitoring Specifications

Eriophorum

3.3 (±2.1) 1. 2.

Polytrichum Moist bog heath

12.6 (±4.0) 3.

0.3 (±0.1) 1.2.

As bare peat Negligible 3.

3.5

7.5 12.5

Very moist bog heath

9.0 3.

0.7 3.

10

Moderately wet Sphagnum hummocks Wet Sphagnum lawn Very wet Sphagnum hollows

Neglected

0.7 (±0.2) 4.

0.5

Neglected

5.2 (±3.2) 3.

5

Neglected

12.8 3.

12.5

5. 6. 7. 8.

Litter accumulation counteracts C losses from degrading peat. Mosses lack roots. With the same water levels, emissions are higher than from bare peat because plant roots change water regime, improve aeration and add labile organic compounds in the form of recently dead roots and root exudates that stimulates the decomposition of more recalcitrant peat. CH4 emissions increase with higher water levels. CH4 emissions from wet bogs in boreal regions are much lower that the values cited here. Published measurements generally show uptake of CO2 from rewetted bog sites. Water bourne carbon export is generally larger before rewetting. The values presented have discarded potential C sequestration and assume zero CO2 flux at rewetted sites.

Maljanen et al (2010). Tuittila et al (1999). Drosler (2005). Bortoluzzi et al (2006).

The proxy indicators are there to provide often tightly correlated inferences about physical variables that have not been measured directly. They allow inferences to be made increasing the interpretational value of datasets to determine how restoration impacts on the wider peatland system.

A2.7. PEAT PHYSICAL CHARACTERISTICS Peat depth and accumulation: Peat depth measurements are recorded comprehensively as part of the Yorkshire Peat Partnership part B survey and provide a base-line dataset for carbon storage calculations in restoration sites. They provide useful information on long-term estimates of peat loss and subsidence or long-term rates of subsidence. By measuring changes in the peat surface against a fixed datum point, peat accumulation will be measured. This is a simple but important measurement that is often overlooked. It can help to inform the overall carbon dynamics of a bog that has undergone restoration. Peat depth methodology: Peat depth measurements will be made at each fixed point quadrat locations and each vegetation quadrat recorded along the belt transect. Simply, drainage rods marked incrementally will be inserted into the peat until the base of the peat deposit impedes any further downward movement. The depth and location will be recorded using GPS. Accumulation methodology: Peat accumulation will be measured at each of the fixed point quadrat locations. A metal plate will be inserted just below the peat surface relative to a datum post fixed into the underlying mineral substratum (Stoneman and Brookes 1997). The top of the fixed datum will remain the 218


Conserving Bogs

A2.7

YPP Survey and Monitoring Specifications

same and peat depth measurement can be taken from surface of the bog to the metal plate. Changes in peat depth will reflect peat accumulation or peat loss. The height difference between the fixed datum and the metal plate will also provide an assessment of peat swelling if measured on a regular basis. Measurement frequencies will be annual alongside vegetation monitoring so the data collected will be more reflective of long-term peat accumulation rates. Texture, colour and humification methodology; For the following 3 sections (7, 8 & 9) a Russian Corer will be used to take a core of each monitoring site, this technique ensures minimal disturbance of the peat profile. The core will be taken on a region of intact blanket bog with reasonable depth which will be determined by peat depth measurements. Russian corers can be inserted quite deeply, the corer is then twisted which opens the chamber and the peat sample is cut producing a core sample measuring 50cm x 5cm. Samples for the three physical characteristics below will be taken from the core and assessed in the field. Peat Texture: Peat texture gives a rapid indication of the type of peat present at each site and to some extent the possible degree of peat degradation. It is a useful proxy measurement for peat classification and therefore will be assessed at each Yorkshire Peat Partnership monitoring site. A quick assessment will be made using the following series of questions; Q1. Is the soil very black, loose and with a low density? Yes = Peat, No = Q2 Q2. Is the soil grey to black; does it bind to form a ball? (Soil may be granular) Yes = Q3, No = Q4 Q3. Is the soil also sandy? Yes = Sandy peat, No = loamy peat Q4. Is the soil grey; does it bind to form a ball that holds together firmly and feels smooth? Yes = Peaty loam, No = Q5 Q5. Is the soil dark coloured but the mineral component dominant? Yes = O-rich other soil, No = other soil Peat colour: The colour of the peat itself can be used to determine to a certain extent its composition. The colour of peat is determined by the following factors; 1). The presence of soil organic matter. Organic matter imparts a dark brown to black colour to the soil. As a general rule, the higher the organic matter content the darker the soil. 2). The oxidation status of the iron compounds in the soil. In more drained and aerated soils Fe (III) minerals give soil a red or yellow colour. In poorly drained soils, iron minerals are reduced and neutral grey coloured minerals predominate. Using the Munsell soil colour chart below a quick assessment of soil colour will be made at each monitoring site. PEAT COLOUR Colour should be assessed using the Munsell Soil Color Chart. Colours shown below are from Hue 7.5YR. RGB values are given to help with accurate colour printing reproduction.

(Extracted from Draft North Pennines AONB Partnership and Natural England National peat depth mapping and storage project, field methodology for peatland survey 2012).

Peat humification; Humification is the measure of the degree of composition; when decomposition and compaction occur the peat gets more humified. Proxies or surrogates can be used to estimate peatland characteristics that may be difficult and expensive to measure in the field. The Von post (1922) scale can be used as a proxy for measuring the degree of peat humification which can be measured using a colorimetric 219


Conserving Bogs

A2.7

YPP Survey and Monitoring Specifications

approach which is usually measured in a laboratory using a colorimetric approach which can be costly and time consuming. There are a number of other methods that can also be used to measure the degree of humification for example spectral laser scanning microscopy. Humification will be measured in situ using the Von Post scale. Technique: Examine samples for plant remains, break open the samples and look also for amorphous material. Squeeze the peat sample and make note of the amount and colour of water that is produced and also how much peat escapes between the fingers. Re-examine the squeezed sample for more evidence of plant material/structure. Consult the scale below to assign degree of humification, H1 (completely undecomposed) - H10 (completely decomposed). Table 16. Simplified version of the Von Post scale for use in the field. For a more detailed description of the Von Post scale see A2.11. Proportion Nature of liquids Decomposition Nature of plant extruded Description expressed on state residues between fingers squeezing None Undecomposed Plant structure Yields only clear unaltered water coloured H1 light yellowbrown None Almost Plant structure distinct Almost clear H2 decomposed yellow-brown None Very weakly Plant structure distinct; Slightly turbid H3 decomposed most identifiable brown None Very weakly Plant structure distinct; Yields strongly H4 decomposed most identifiable turbid water Very little Moderately Plant structure clear Strongly turbid, decomposed but becoming contains a little H5 indistinct peat in suspension One-third Well decomposed Plant structure Muddy, much H6 indistinct peat in suspension One-half Strongly Indistinct with few Strongly muddy H7 decomposed remains identifiable Two-thirds Very strongly Very indistinct, only Thick mud, little H8 decomposed plant fibres and wood free water identifiable Nearly all Almost Plant structure almost No free water H9 completely unrecognisable decomposed All Completely Completely amorphous No free water H10 decomposed (Extracted from draft North Pennines AONB Partnership and Natural England National peat depth mapping and storage project, field methodology for peatland survey 2012). Finally, the table below shows how the integration of multiple variables such as peat physical characteristics, vegetation and topography can inform about peatland dynamics to a much greater extent than focusing solely on keystone species.

220


Conserving Bogs

A2.7

YPP Survey and Monitoring Specifications

Table 17. Categories of peat based on function and their relation to vegetation management, water table and organic matter dynamics. Peat category Active

Structure, vegetation and management Semi-natural vegetation cover of bog mosses, cotton grasses and dwarf shrubs. Could include purple moor grass dominated vegetation in some circumstances. Bogs are diplotelmic in structure with a true acrotelm of living bog mosses. Semi-natural vegetation but with a balance of gramimoids/forbs/ericoids and bryophytes changed by adverse/lack of management. Acrotelm absent or impacted. Associated with burning, drainage, afforestation of peatland.

Water table

Organic matter dynamics

Water table mostly fluctuates within acrotelm rooting zone. Catotelm remains permanently waterlogged.

OM fixed and starts to degrade in acrotelm releasing some CO2.

Water table fluctuates within previously accumulated catotelm peat. Taller vegetation draws water from peat surface layers.

Bare

No true acrotelm or vegetation. Associated with peat cutting, wildfire, pollution, overstocking or cultivation of peatlands. Some erosion complexes are longstanding and apparently natural.

Archaic

No true acrotelm, agricultural vegetation including cultivated land. Usually deep drained and forestry where no bog flora remains. Usually deep drained.

Water table fluctuates within the previously accumulated catotelm peat. Upstanding dry hags alternate with lower wetter but periodically dehydrated peat. Water table controlled by ditch systems, often with underdrainage. Held typically at ~4080cm below peat surface in the catotelm.

Falling litter degrades at the peat surface, little new organic matter reaches are of permanent waterlogging. Upper catotelm peat degrades into CO2 and becomes more decomposed. More CH4 is oxidised in upper peat layers, can be subject to peat shrinkage. No new litter entering the system. Catotelm peat degrades into CO2 but extremes of temperature probably retard degradation.

Wasted

No true acrotelm or catotelm. Most peat has been lost or removed.

Degraded

Water table mainly fluctuates within underlying mineral soils.

Based on Lindsay and Immirzi (1996) as reported in JNCC (2011).

221

Plant litter degrades at peat surface. Upper catotelm degrades into CO2 and becomes more decomposed. Little CH4 released; dry surface peat may oxidise atmospheric CH4. Peat surface rapidly lowers due to decomposition and erosion. Peat organic matter increasingly mixes with soil mineral material. Decomposition of organic matter slows releasing less CO2. Little CH4 released and some atmospheric CH4 oxidised.


Conserving Bogs

A2.8

YPP Survey and Monitoring Specifications

A2.8. MONITORING CONSIDERATIONS It is important to take into consideration the physical impact of monitoring itself may have on the sampling site and the subsequent impact it may have in any trends or changes that may occur on your monitoring sites. When using marker posts it is important to make sure that they will not serve as a perch for birds. This can introduce nitrogen, phosphorous and seeds to the monitoring area which will, in turn, influence revegetation rates and the type of vegetation that establishes in the monitoring area. It is vital that trampling in the peatland environment is avoided even if sampling frequency is as low as once a year. Sphagnum can not tolerate any level of trampling and will either be lost or will fail to establish so it is vital that measures are taken to avoid disruption of the site. There are simple measures that can be taken in order to ameliorate the effect of sampling disruption on a restoration site: ď&#x201A;ˇ

Use suitable low impact footwear (snow shoes were recommended by Richard Lindsay pers comm.) when near fixed point locations.

ď&#x201A;ˇ

Have a raised board walk to stand or sit on when undertaking the sampling. There are many different methods than can be employed for this purpose, along as it minimises disruption in the monitoring area.

A2.9. REMOTE MONITORING Alongside practical vegetation monitoring, remote analysis of trends in vegetation changes and other variables will also be implemented. This will include pre-monitoring of existing data sets which currently consist of 2002/02 and 2008/09 aerial photographs and 2008/09 infra red imagery. Sequential changes in vegetation, extent of bare peat, grip and gully characteristics will be quantified using spectral analysis software. All bare peat, grips and gullies are digitised and quantified using GIS as an initial part of the Yorkshire Peat Partnership pre-restoration protocol (See Appendix 1). Vegetation community, bare peat category, cause of bare peat, burning category and Sphagnum presence/absence are recorded on- site as part of the second stage of the pre-restoration protocol. These data will provide a base-line data set where trends in relation to restoration can be analysed. The methodology for the continuation of this data set post restoration is detailed in a separate restoration monitoring protocol. Fixed point photography will provide the basis for post restoration remote monitoring. Photographs will taken ensuring a fixed point standardised format approach. Photographs will be scanned and GIS compatibility ensured. Manual digitisation and spectral analysis will be applied to quantify changes in the environmental variables as listed above. Over time, this will enable sequential analysis of any trends in relation to restoration to be quantified.

A2.10. OVERALL SUMMARY The overall aim of the protocol is to assess how successful restoration has been in meeting restoration objectives. The monitoring techniques chosen are closely linked to restoration goals which will help us to interpret direct changes in relation to restoration which can inform further work. The use of proxyâ&#x20AC;&#x2122;s will enable interpretation of other environmental variables that cannot be directly measured within the scope of the monitoring protocol. The protocol is designed to be implemented by skilled volunteers to ensure longterm, accurate and functional restoration monitoring. 222


Conserving Bogs

A2.11

YPP Survey and Monitoring Specifications

Additional biodiversity indicators: This section aims to give a brief description of additional biodiversity indicators that can be monitored to assess the impact of restoration on the biodiversity of the peatland habitat. They are not currently included in the Yorkshire Peat Partnership protocol but opportunities to deploy additional monitoring are sought. Birds: Blanket bogs support birds that are unique in regards to their breeding populations and some rarity. It can be useful to survey birds as they may be indicators and contributors to habitat quality, populations can also alter rapidly as a response to changes in management. Birds represent flagship species and they are useful for project promotion. Standard techniques include the Common Bird Census, the Breeding Bird Survey and the Wetlands Bird Survey. There are a number of ways to conduct bird surveys such as direct counts, transect counts and netting. Invertebrates: Blanket bog is extremely important to many species of invertebrate and they are essential to the diet of many upland bird species. They are also integral to the debate around the effect of upland restoration techniques such as grip blocking on grouse chick populations as they are dependant on invertebrates as a food source. Hoverflies and crane flies are particularly associated with blanket bog habitat. However, expertise required for identification is high, monitoring frequency and density is also high. Consequently, monitoring of invertebrate populations can be labour intensive and costly. Invertebrates populations have been deemed as an important monitoring tool for restoration but may have to be undertaken as localised studies as part of a research objective. Microorganisms: The peatland microbial community is a vital ecosystem component; governing decomposition, greenhouse gas production and water quality are just a few examples amongst many other functions. Monitoring changes in microbes and the microbial community could therefore shed light on restoration success. There are a number of different techniques that can be used to quantify peat microbial community profiles, but they are extremely expensive and they are technically challenging, requiring a high degree of expertise. As a result, studies assessing restoration and microbial activity are usually confined to site specific research projects.

A2.11. DETAILED VON POST SCALE FOR CLASSIFICATION OF HUMIFICATION H1 - Completely undecomposed peat which, when squeezed, releases almost clear water. Plant remains easily identifiable. No amorphous material present. H2 - Almost entirely undecomposed peat which, when squeezed, releases clear or yellowish water. Plant remains still easily identifiable. No amorphous material present. H3 - Very slightly decomposed peat which, when squeezed, releases muddy brown water, but from which no peat passes between the fingers. Plant remains still identifiable, and no amorphous material present. H4 - Slightly decomposed peat which, when squeezed, releases very muddy dark water. No peat is passed between the fingers but the plant remains are slightly pasty and have lost some of their identifiable features. H5 - Moderately decomposed peat which, when squeezed, releases very â&#x20AC;&#x153;muddyâ&#x20AC;? water with a very small amount of amorphous granular peat escaping between the fingers. The structure of the plant remains is quite indistinct although it is still possible to recognize certain features. The residue is very pasty. H6 - Moderately highly decomposed peat with a very indistinct plant structure. When squeezed, about onethird of the peat escapes between the fingers. The residue is very pasty but shows the plant structure more distinctly than before squeezing. H7 - Highly decomposed peat. Contains a lot of amorphous material with very faintly recognisable plant structure. When squeezed, about one-half of the peat escapes between the fingers. The water, if any is released, is very dark and almost pasty. H8 Very highly decomposed peat with a large quantity of amorphous material and very indistinct plant structure. When squeezed, about two-thirds of the peat escapes between the fingers. A small quantity of 223


Conserving Bogs

A2.12

YPP Survey and Monitoring Specifications

pasty water may be released. The plant material remaining in the hand consists of residues such as roots and fibres that resist decomposition. H9 Practically fully decomposed peat in which there is hardly any recognizable plant structure. When squeezed it is a fairly uniform paste. H10 Completely decomposed peat with no discernible plant structure. When squeezed, all the wet peat escapes between the fingers.

A2.12. DATA TRANSFER, STORAGE AND MANIPULATION YPP is undertaking a series of core measurements as part of survey and monitoring protocols. Data requirements should be an integral part of the protocols and should include specifications of the variables. Database Management All data generated by YPP will be managed on a Microsoft Access. This has been selected because it supports data storage and transfer requirements, data can be easily exported as other file formats if required (e.g. easily transferred to excel and R if graphical and/or statistical manipulation requirements) and is widely available for use. Microsoft Access Microsoft Access is user-friendly and does not require prior programming knowledge, this is essential if data entry is being done by volunteers without advanced database management knowledge. Security settings can also be used so that only certain elements of the database can be accessed by certain users, this will ensure data security. Microsoft Access permits multiple users to share and update data without overwriting each others work and data can be locked at the entry level. Data can be imported and exported to and from many formats including excel (graphical manipulation) and R (statistical manipulation) and it has the ability to link data and use it for viewing, querying, editing, analysis and reporting. More advanced applications allow users to query data which can be viewed graphically and macros can also be deployed in order to programme specific commands if desired. Data transfer; GPS to database Data is currently downloaded from the mobile mapper directly to MapInfo as MapInfo tab so spatial representation of data can be instantly mapped. The associated MapInfo data table can be easily converted from MapInfo to excel as a CVS delimited file. The excel file can then be easily converted and exported into Access. All data conversion steps can be easily automated so advanced knowledge will not be required at any stage of the process. Written methodologies will be created for each step of the process and hyperlinked within an instruction manual. Application of statistics In order to establish the samples size e.g. number of quadrats to record or the number of dipwells to install on a site in order to generate statistically meaningful data a power analysis can be performed on sample design. Power analysis can be performed “a priori” so as to ensure adequate sample size before monitoring is instigated. The overall basic question that power analysis can determine is “How many observations do you require in order to get the information that you require from your study”. Power analysis will be performed on all protocols in order to establish the minimum sample size required in order to ensure that data trends can be interpreted successfully. 224


Conserving Bogs

A2.12

YPP Survey and Monitoring Specifications

The Yorkshire Peat Partnership will adopt trajectory analysis for establishing restoration “success”. Determinants of restoration success have been assessed and can be broadly summarised in to the following categories;    

To improve the hydrological integrity of the peatland. To establish bog vegetation on areas of bare peat. To reduce the amount of water flowing through grips and gullies using blocking techniques. To reduce the amount of carbon being lost from the peatland system by a combination of the above determinants.

The monitoring data generated by YPP will be subject to trajectory analysis. This is for data that is collected periodically from field sites (usually represent relatively large data sets). It is used to interpret data that is recorded from a site periodically and are plotted to establish trends over time. There are a number of statistical techniques that can be used in trajectory analysis including regression analysis, time series plots and trend analysis. The most appropriate technique will be applied following an assessment of recorded data. It has been established that the protocol for vegetation monitoring is designed so that trajectory analysis can be applied to the data sets generated.

225


Conserving Bogs

YPP Survey and Monitoring Specifications

A2.13

A2.13. SITE DETAILS RECORDING FORM

Site Name: Region:

Site Information Grid ref: Weather conditions:

Survey date: Owner: Address: Risk assessment completed and signed? Permission/access issues?

Notable species seen whilst monitoring?

Any additional comments?

226


Conserving Bogs

YPP Survey and Monitoring Specifications

A2.14

A2.14. PEAT PHYSICAL PROPERTIES FIELD FORM

Fill in the field form below at each point where a core is taken. For each site a minimum of two cores is desirable, preferably from a more degraded and a more intact part of the site for comparison. A third core can be taken if deemed necessary. The two table display codes to enter in the veg community column (Table 1) and the evidence of column (Table 2). Use a best estimate to determine which category the variables relate to. Table 18. Vegetation Community Comm BB75 HD NCG BF

Veg Description Blanket bog >75% dwarf shrub Dry heath Neutral/calcareous grassland Basic Fen

Comm BB50 WD BR BP

Veg Description Blanket bog â&#x2030;Ľ25%-â&#x2030;¤75% dwarf shrub Wet heath Bracken Bare peat

Comm BB25 AG AF BM

Veg Description Blanket bog <25% dwarf shrub Acid grassland (Molinia, Juncus, Nardus) Acidic Fen Bare mineral

Table 19. Evidence of Damage Cat D P

Description/Evidence of Drainage People

Cat L F

Description/Evidence of Livestock Freeze/thaw

Cat R W

Description/Evidence of Rabbits Wind

Table 20 Evidence recording Form. Fill in the form below using the tables above to inform vegetation and evidence categories and use the nanotope guide provided to assess which nanotope zone the core is extracted from. Additionally, use guides provided to assess colour, texture and humification. Recorder/site:

Weather: **Evidence of:

GPS/Grid ref:

Core no:

*Veg community

Nanotope

Degraded/intact?

1 2 3 Recorder/site:

Weather: **Evidence of:

GPS/Grid ref:

Core no:

*Veg community

Nanotope

Degraded/intact?

1 2 3 Recorder/site:

Core peat depth cm

Weather: **Evidence of:

GPS/Grid ref:

Core no:

Core peat depth cm

*Veg community

Nanotope

Degraded/intact?

Core peat depth cm

1 2 3

227

Core 1: Core 2: Rod peat depth cm

Core 1: Core 2: Rod peat depth cm

Core 1: Core 2: Rod peat depth cm

Colour

Colour

Colour

Texture

Texture

Texture

Humification

Bulk density sample? Y/N

Humification

Bulk density sample? Y/N

Humification

Bulk density sample? Y/N


Conserving Bogs

YPP Survey and Monitoring Specifications

A2.15

A2.15. VEGETATION HEIGHT RECORDING FORM Date: Shrub Layer cm

1

2

3

Location: 4

Herb Layer cm

1

2

3

Surveyor: 4

Quadrat 1 mean Shrub Layer cm

1

2

3

4

Quadrat 1 mean Herb Layer cm

1

2

3

4

1

2

3

4

Quadrat 2 mean Shrub Layer cm

1

2

3

4

Quadrat 2 mean Herb Layer cm

Quadrat 3 mean Shrub Layer cm

1

2

3

4

Quadrat 3 mean Herb Layer cm

1

2

3

4

Quadrat 4 mean Shrub Layer cm

1

2

3

4

Quadrat 4 mean Herb Layer cm

1

2

3

4

Quadrat 5 mean Shrub Layer cm

1

2

3

4

Quadrat 5 mean Herb Layer cm

1

2

3

4

Quadrat 6 mean

Quadrat 6 mean

Table 21 Height recording sheet: The purpose of this sheet is to record the height of the top 3 most dominant species at each layer. If less than 3 species are present then record species that are present. The quadrat will be visually split into quarters and the height of the tallest plant for each species will be noted in each of the quarters in order to obtain a mean height in cm over the whole quadrat.

228


Conserving Bogs

YPP Survey and Monitoring Specifications

A2.16

A2.16. VEGETATION SPECIES RECORDING FORM

Shrub Layer Common heather Cross leaved heath Bilberry Crowberry Cowberry Bog Rosemary Bog myrtle

1

2

3

4

Herb Layer Common cotton grass Hareâ&#x20AC;&#x2122;s tail cotton grass Wavy hair cotton grass Moor matt grass

1

2

4

Moss layer Sphagnum papillosum Sphagnum fallax Sphagnum capillifolium Sphagnum cuspidatum Sphagnum subnitens

Purple moor grass Bog asphodel

Sphagnum magellanicum Sphagnum palustre Sphagnum fibriatum Sphagnum angustifolium Sphagnum denticulatum Sphagnum flexuosum

Cloudberry Heath bedstraw Common tormentil Velvet bentgrass Creeping bentgrass Bracken fern Narrow buckler fern Common sedge Carnation sedge Bottle sedge Sheeps fescue

Sphagnum tellenum Sphagnum fuscum Sphagnum inundatum Sphagnum molle Sphagnum affine Sphagnum quinquefarium Sphagnum recurvum

Creeping soft grass Sweet vernal grass Heath rush Soft rush Other variables % Brashed ground rock/mineral Bare peat Standing water Grouse dropping p/a Dead vegetation Burnt vegetation Mown Y/N % shrub cover

3

Other mosses Hypnum spp Polytrichum commune Polytrichum spp

Sharp flowered rush Lesser twayblade

Campylopus spp

Lousewort Sheeps sorrell Rosebay willow herb

Rhytidiadelphus spp Dicranium spp Pluerozium spp Other spp Liverwort spp Lichen spp Flapwort spp % moss cover

% herb cover

229

1

2

3

4


Conserving Bogs

YPP Survey and Monitoring Specifications

Table 22 Vegetation Species recording sheet.

A2.17. SUMMARY OF NANOTOPES AND LANDSCAPE RECORDING

A2.17

Microtope/Nanotope analysis â&#x20AC;&#x201C; Summary of microtopes/nanotopes. Nanotope analysis will be made in conjunction with fixed point quadrat analysis Zone Microtopography/plant species Zone Microtopography/plant species E1 Revegetation of gully or section of gully. T3 Some moss species, little Sphagnum, possibly Calluna. E2 Gully actively eroding, no sig. revegetation T2 Sphagnum ground cover variable, dwarf shrubs dominate. Em1/2 Evidence of impact on bog surface, grazing, T1 Richest Sphagnum and bog spp. Zone, less burning etc. Calluna. Tk Formerly eroded but undergoing sig. A1 Spp poor, dominated by S. Cuspidatum, revegetation possible cotton grass. T4 Hags; several heathland spp., 1 or 2 bog species, A2 Shallow pools <20cm deep, moss cover lichens, dwarf shrubs. limited, possible vascular plants, possible decomposed vegetation at base.

Table 23 Summary of nanotopes. Date: Surveyor: Quadrat no.

Location:

Nanotope

Approx extent m2

Photo ID

Time

Brief quadrat summary e.g. hummocky, elevated, flat, eroded etc.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Table 24 Landscape details recording form.

230

Peat depth cm


Conserving Bogs

YPP Survey and Monitoring Specifications

231


Conserving Bogs

YPP Survey and Monitoring Specifications

232

Conserving bogs  

The Management Handbook

Conserving bogs  

The Management Handbook

Advertisement